(CNN) Iraqi forces have regained control of the airport in Mosul, part of a monthslong operation to push ISIS militants from the key city.

The airport -- largely destroyed by ISIS forces -- is now fully under Iraqi Federal Police control, said Col. Abdel Amir Mohamed, commander of the rapid response unit of the Federal Police.

Brett McGurk, the US envoy for the anti-ISIS coalition, congratulated Iraq for the victory.

"Congratulations to Iraqi forces for completing complex maneuver ops to secure #Mosul airport from #ISIS terrorists," he tweeted. "#ISIS is now trapped."

Congratulations to Iraqi forces for completing complex maneuver ops to secure #Mosul airport from #ISIS terrorists. #ISIS is now trapped.

British Major Gen. Rupert Jones, deputy commander of Operation Inherent Resolve, offered a more muted assessment of the situation on the ground, telling CNN's Christiane Amanpour the airport was "reasonably well-secured."

"It's been a really good day," said Jones, speaking from Baghdad on Thursday. "The Iraqis are on the airfield. It looks reasonably well-secured."

"We should just be a little bit patient. It will really be for the Iraqis to say for certain once they're confident they're holding it," he added.

Iraqi forces launched a new bid to retake the western parts of the city on Sunday after declaring in late January that the east had been liberated.

Latest developments

Warplanes bombed ISIS positions in the cities of Qaim and Hawija, as well as the Mansour district of western Mosul, killing at least 85 militants.

Joint Operations Command says forces "killed many ISIS militants" and defused 60 IED.

Iraqi forces have faced ISIS suicide car bombs and improvised explosive devices.

Counterterrorism forces have stormed the al-Ghazlani military base west of the airport.

There has been heavy fighting between Iraqi forces and ISIS at Mosul's main electrical power station.

Residents say ISIS is searching homes for cell phones.

Residents from eastern Mosul, under Iraqi control, send letters of support to the residents in the west.

Federal police and rapid response forces, backed by drones and heavy artillery, advanced from several positions to storm the airport, Lt. Gen. Raid Shakir Jaudat said in a statement. ISIS has held the airport since 2014 and has largely destroyed its infrastructure.

Sources have told CNN in recent months that ISIS has sabotaged the airstrip there to prevent its use.

The airport is on a large area of land in that city that is a symbolically important target for Iraqi forces. The area is an access point into the city from the southwest of the country. Taking it puts Iraqi forces in control of an area on the river's west bank for the first time.

Forces took the airport in a few hours and appear to be moving swiftly, taking back control of two villages -- Yarmouk and Tal al-Rayan -- near the airport and the al-Ghazlani military camp.

They have also taken control of an ISIS weapons storage warehouse, former ISIS headquarters and the barracks at al-Ghazlani, Brig. Gen. Yahya Rasoul, a spokesperson for the Iraqi operation, told CNN.

On top of that, the Joint Operations Command center reported that forces "destroyed many ISIS vehicles," defused 60 improvised explosive devices and "killed many ISIS militants."

But the push to take western Mosul is expected to take some time -- the east of the city took more than three months to take from ISIS control.

A city split

A resident of western Mosul told CNN that groups of ISIS fighters had been searching homes in one neighborhood near the river's bank, looking for cell phones and residents using them. ISIS forbids the use of cell phones and has executed residents in the past for using them.

ISIS frequently accuses residents of passing information to Iraqi security forces, and metes out harsh punishment to people caught using phones.

The east and west is divided by the Tigris River, and US-led coalition airstrikes have damaged all five bridges connecting the two sides in an effort to contain the militants in the west.

Photos: Mosul: Iraqi-led forces push into key city Members of the Iraqi federal police wave the country's flag as they celebrate in the Old City of Mosul on July 9, 2017. Iraq declared victory against ISIS forces in Mosul after a grueling monthslong campaign. The battle to reclaim Mosul, the last major ISIS stronghold in Iraq, has been underway since fall 2016. Hide Caption 1 of 73 Photos: Mosul: Iraqi-led forces push into key city This injured girl was found by Iraqi forces as they advanced against ISIS militants in the Old City of Mosul on Monday, July 3. She was carried away for medical assistance. Hide Caption 2 of 73 Photos: Mosul: Iraqi-led forces push into key city A suspected ISIS fighter is held in a basement while Iraqi forces continue to push for control of the Old City of Mosul on Monday, July 3. Hide Caption 3 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi Special Forces soldier exchanges fire with ISIS militants in the Old City on Friday, June 30. Hide Caption 4 of 73 Photos: Mosul: Iraqi-led forces push into key city A bomb explodes near the al-Nuri mosque complex on Thursday, June 29. Iraq's military has seized the remains of the Great Mosque of al-Nuri. Iraq and the United States have accused ISIS of blowing up the historic mosque. Hide Caption 5 of 73 Photos: Mosul: Iraqi-led forces push into key city Members of the Iraqi Federal Police hold a position as US-led coalition forces advance through the Old City on Wednesday, June 28. Hide Caption 6 of 73 Photos: Mosul: Iraqi-led forces push into key city The remnants of Mosul's ancient leaning minaret are seen in the Old City on Sunday, June 25. ISIS' claim that US warplanes were responsible for the destruction of the minaret is "1,000% false," US officials told CNN. Hide Caption 7 of 73 Photos: Mosul: Iraqi-led forces push into key city Two boys comfort each other after their home collapsed during fighting between Iraqi forces and militants in Mosul on Saturday, June 24. The boys, who are cousins, said some of their relatives were still under the rubble. Hide Caption 8 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi soldier helps transport a girl as residents flee their homes west of Mosul on Friday, May 26. Hide Caption 9 of 73 Photos: Mosul: Iraqi-led forces push into key city Displaced Iraqis make their way through rubble after evacuating their homes in a neighborhood of west Mosul on Wednesday, May 17. Hide Caption 10 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi man tries to extinguish a burning car during fighting in Mosul's western Rifai neighborhood on Tuesday, May 16. Hide Caption 11 of 73 Photos: Mosul: Iraqi-led forces push into key city A member of the Iraqi counterterrorism service secures a building as troops push toward Mosul's Al-Oraibi western district on Sunday, May 14. Hide Caption 12 of 73 Photos: Mosul: Iraqi-led forces push into key city A smoke cloud rises on the front line as the Iraqi Emergency Response Division advances in west Mosul on Saturday, May 6. Hide Caption 13 of 73 Photos: Mosul: Iraqi-led forces push into key city A wounded man is transported in western Mosul on Friday, April 21. Hide Caption 14 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi federal policeman smokes during a break from battle on Wednesday, April 12. Hide Caption 15 of 73 Photos: Mosul: Iraqi-led forces push into key city A member of Iraq's security forces stands guard in eastern Mosul as smoke rises from the ISIS-controlled western section of the city on Friday, April 7. Hide Caption 16 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqis visit a bath house on the southern outskirts of Mosul on Wednesday, April 5. Hide Caption 17 of 73 Photos: Mosul: Iraqi-led forces push into key city Flames billow from an explosion in Mosul during a clash between Iraqi forces and ISIS fighters on Sunday, March 5. Hide Caption 18 of 73 Photos: Mosul: Iraqi-led forces push into key city Families are forced to evacuate as Iraqi forces advance in western Mosul on Thursday, March 2. The number of internally displaced people has surged as the offensive effort has intensified. Hide Caption 19 of 73 Photos: Mosul: Iraqi-led forces push into key city Mosul residents cross a damaged bridge in the al-Sukkar neighborhood on Saturday, January 21. Hide Caption 20 of 73 Photos: Mosul: Iraqi-led forces push into key city French President Francois Hollande and French Defense Minister Jean-Yves Le Drian, right, view territory held by ISIS during a visit to a military outpost near Mosul on Monday, January 2. Hide Caption 21 of 73 Photos: Mosul: Iraqi-led forces push into key city A young girl takes part in a Christmas Day Mass at a church in the predominantly Christian town of Qaraqosh. The area's churches were heavily damaged by ISIS militants before the town was freed by Iraqi forces during the Mosul offensive. Hide Caption 22 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi Shiite fighters ride through a desert area near the village of Al-Boutha al-Sharqiyah, west of Mosul, on Friday, December 2. Hide Caption 23 of 73 Photos: Mosul: Iraqi-led forces push into key city Internally displaced Iraqis who fled the fighting in Mosul watch as a civilian drone films them at the al-Khazir camp on Thursday, December 1. Hide Caption 24 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi soldier searches a home for ISIS militants after Iraqi forces retook the village of Al-Qasr on Wednesday, November 30. Hide Caption 25 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi soldiers transport a comrade who was injured during a battle near the village of Haj Ali on Tuesday, November 29. Hide Caption 26 of 73 Photos: Mosul: Iraqi-led forces push into key city A man mourns during the funeral of four Iraqi paramilitary fighters who were killed in battles in the town of Tal Afar. Hide Caption 27 of 73 Photos: Mosul: Iraqi-led forces push into key city Displaced civilians return to the village of Tall Abtah on Friday, November 25, after Iraqi forces retook the village from ISIS. Hide Caption 28 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi civilians sit on the ground in Mosul on November 24. An Iraqi officer addressed the group, demanding to know the whereabouts of alleged ISIS militants who opened fire on troops a few days earlier. Hide Caption 29 of 73 Photos: Mosul: Iraqi-led forces push into key city An injured baby receives treatment at a field hospital in Mosul on November 15. Hide Caption 30 of 73 Photos: Mosul: Iraqi-led forces push into key city A woman cries Sunday, November 13, after seeing the St. Addai church that was damaged by ISIS fighters during their occupation of the Keramlis village. Hide Caption 31 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi special forces soldier prays next to a Humvee before troops pushed toward Mosul's Karkukli neighborhood on November 13. Hide Caption 32 of 73 Photos: Mosul: Iraqi-led forces push into key city A Kurdish Peshmerga fighter holds part of a defused bomb planted by ISIS militants in Bashiqa, Iraq, on Friday, November 11. Hide Caption 33 of 73 Photos: Mosul: Iraqi-led forces push into key city A member of Iraq's special forces guards two suspected ISIS fighters found hiding in a house in Mosul on November 11. Hide Caption 34 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi woman displaced by war holds her cat near a checkpoint in the Iraqi village of Shaqouli, east of Mosul, on November 10. Hide Caption 35 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi troops watch a broadcast of Donald Trump's acceptance speech in a house in Arbid, on the outskirts of Mosul, on Wednesday, November 9. Iraqi Prime Minister Haider al-Abadi congratulated Trump on his win and said he hoped for continued support in the war on ISIS. Hide Caption 36 of 73 Photos: Mosul: Iraqi-led forces push into key city US Marines install equipment at a coalition base in Qayyara on November 9. Hide Caption 37 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi forces member investigates a mass grave that was discovered after coalition forces recaptured the area of Hamam al-Alil on Monday, November 7. Hide Caption 38 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi children witness a man being interrogated by a member of the Iraqi army at a base next to the Al-Intissar neighborhood of Mosul on November 7. Hide Caption 39 of 73 Photos: Mosul: Iraqi-led forces push into key city A civilian man who fled the fighting trims his beard after reaching an Iraqi army position in Mosul on November 7. Hide Caption 40 of 73 Photos: Mosul: Iraqi-led forces push into key city Children play in debris created by an airstrike in Qayyara on Sunday, November 6. Hide Caption 41 of 73 Photos: Mosul: Iraqi-led forces push into key city Female members of the Freedom Party of Kurdistan sing as they hold a position near Bashiqa on November 6. Hide Caption 42 of 73 Photos: Mosul: Iraqi-led forces push into key city A baby is passed through a fence back to his mother at a refugee camp in the Khazir region on Saturday, November 5. Hide Caption 43 of 73 Photos: Mosul: Iraqi-led forces push into key city People line up to receive food at a refugee camp in the Khazir region on November 5. Thousands are taking refuge in camps set up for internally displaced people. Hide Caption 44 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi soldiers pass near a bridge destroyed in an airstrike in Qayyara on November 5. Hide Caption 45 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi soldiers patrol an alley on the outskirts of Mosul on Friday, November 4. Hide Caption 46 of 73 Photos: Mosul: Iraqi-led forces push into key city A suspected member of ISIS is detained at a checkpoint near Bartella, Iraq, on November 4. Hide Caption 47 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi families pack into a truck to be moved to camps on Thursday, November 3. Hide Caption 48 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi special forces soldier searches for the location of an ISIS sniper in Gogjali on November 1. Hide Caption 49 of 73 Photos: Mosul: Iraqi-led forces push into key city A man fleeing the village of Bazwaya carries a white flag as he arrives at a checkpoint on November 1. Hide Caption 50 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi soldier receives treatment after being injured during clashes with ISIS fighters near Bazwaya on October 31. Hide Caption 51 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi soldier navigates through a shattered windshield as coalition forces advance on Bazwaya on October 31. Hide Caption 52 of 73 Photos: Mosul: Iraqi-led forces push into key city Archbishop Yohanna Petros Mouche, center, performs Mass in the liberated town of Qaraqosh on Sunday, October 30. Hide Caption 53 of 73 Photos: Mosul: Iraqi-led forces push into key city Children play in a camp for internally displaced people near Kirkuk, Iraq, on October 30. More than 600 families from Tel Afar, a town west of Mosul, have been living in the camp since ISIS took control of the area in 2014. Hide Caption 54 of 73 Photos: Mosul: Iraqi-led forces push into key city Displaced families are seen on the road near Qayyara on Saturday, October 29. Hide Caption 55 of 73 Photos: Mosul: Iraqi-led forces push into key city U.S. military personnel take cover in a bunker after a mortar alarm was sounded at a coalition air base in Qayyara on Friday, October 28. Hide Caption 56 of 73 Photos: Mosul: Iraqi-led forces push into key city Women and children grieve over the grave of a family member at a Qayyara cemetery damaged by ISIS on October 27. Hide Caption 57 of 73 Photos: Mosul: Iraqi-led forces push into key city Residents of Qayyara wait for distribution of food and water rations on October 26. Local water sources have been contaminated by the burning oil and sulfur. Hide Caption 58 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraq's counterterrorism forces advance toward ISIS positions in Tob Zawa on October 25. Hide Caption 59 of 73 Photos: Mosul: Iraqi-led forces push into key city Soldiers give first aid to an injured boy in Tob Zawa on October 25. Hide Caption 60 of 73 Photos: Mosul: Iraqi-led forces push into key city Kurdish Peshmerga forces take positions as they start to move toward the Imam Reza and Tizxirab villages of the Bashiqa district on Sunday, October 23. Hide Caption 61 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi forces distribute fruit in the village of al-Khuwayn, south of Mosul, after recapturing it from ISIS on October 23. Hide Caption 62 of 73 Photos: Mosul: Iraqi-led forces push into key city Kurdish security forces detain a suspected member of ISIS in the eastern suburbs of Kirkuk on Saturday, October 22. Hide Caption 63 of 73 Photos: Mosul: Iraqi-led forces push into key city An Iraqi forces member helps a man push a car as they arrive at a refugee camp in Qayyara on October 22. Hide Caption 64 of 73 Photos: Mosul: Iraqi-led forces push into key city Spent bullet cartridges litter the street around the Jihad Hotel, where ISIS militants battled Iraqi security forces in Kirkuk on Friday, October 21. Hide Caption 65 of 73 Photos: Mosul: Iraqi-led forces push into key city Gen. Abdel Ghani al-Asadi, who leads Iraq's counterterrorism forces, sits in Bartella on October 21 after the town was reclaimed. Hide Caption 66 of 73 Photos: Mosul: Iraqi-led forces push into key city Peshmerga fighters look over a village during an assault near Bashiqa on Thursday, October 20. Hide Caption 67 of 73 Photos: Mosul: Iraqi-led forces push into key city Iraqi forces head toward the front lines near Qayyara on Tuesday, October 18. Hide Caption 68 of 73 Photos: Mosul: Iraqi-led forces push into key city A Peshmerga fighter peers up from an underground tunnel in the liberated town of Badana on October 18. ISIS fighters have built tunnels below residential streets to escape from airstrikes. Hide Caption 69 of 73 Photos: Mosul: Iraqi-led forces push into key city Kurdish security forces take up a position near ISIS-controlled villages on Monday, October 17. Hide Caption 70 of 73 Photos: Mosul: Iraqi-led forces push into key city Smoke rises from a suicide car bomb attack carried out by ISIS in the village of Bedene on October 17. Hide Caption 71 of 73 Photos: Mosul: Iraqi-led forces push into key city Members of the Iraqi coalition gather around a fire at Zardak mountain ahead of the offensive. Hide Caption 72 of 73 Photos: Mosul: Iraqi-led forces push into key city Peshmerga forces deploy in the dark near the village of Wardak early on October 17. Hide Caption 73 of 73

Residents of eastern Mosul have written letters of solidarity that the Iraqi Air Force dropped over western neighborhoods on Wednesday.

CNN went aboard an Air Force plane and met two residents of the east who had written some of the letters. One, Ghassan Mohammed Saadoun, said that he had received similar reassuring letters from other Iraqis when the east was being liberated.

He said ISIS had tried to confiscate those letters.

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"I have lived that experience and seen these letters and leaflets, but ISIS tried to prevent us from seeing them as much as they can. When that happened, the children of ISIS went out into the streets and collected these letters early in the morning hours so no one could read them," he said.

One of the letters read: "Do not be afraid of the security forces -- they are coming to protect and to liberate you from injustice. Collaborate with them and don't be afraid of them. They are your sons. We wish you safety and security."

Another read: "We ask Allah to ease the pain that you are in. We pray to Allah to protect you. We ask you to please stay indoors for your safety when security forces arrive in your areas. Allah bless you our people."

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Rights groups fear high death toll

Iraqi commanders say the battle for western Mosul will be the toughest fight yet against ISIS. Over the past two years, the militant group has dedicated much of its defensive preparation to the western part of the city.

The city has networks of alleys that are impassable by military vehicles. Human rights organizations fear that the use of heavy weaponry in the narrow streets of the old city -- where an estimated 650,000 civilians are still trapped -- would probably result in very high human toll.

Meanwhile, US troops operating around Mosul have been in exchanges of fire with ISIS, and some have been wounded in the last six to eight weeks as they have pushed closer to key front lines, military officials acknowledged.

A US defense official confirmed some had been injured on the battlefield, but declined to give numbers, saying that the injured had been evacuated from the battlefield.

The offensive to retake Mosul began in October in an extraordinary union of Iraqi troops and militia representing minority ethnic and religious groups that have often stood on opposing sides in Iraq's history.