Thousands of letters of love and hope have been dropped on western Mosul amid fears for an estimated 750,000 civilians trapped in Isis-held parts of the city.

One letter uncovered by reporters embedded with Iraqi troops was from a man called Omar, who was writing to his family and friends from a retaken district of the city.

“I just want to let you know what we are safe here,” it said. “I hope your areas will be liberated by government forces as soon as possible and be free from Isis fighters.”

The hand-written message urged loved ones not to go outside during fighting, according to a translation by the New York Times, and was signed off with: “We are all Iraq, I love you.”

It was among four million letters dropped over Isis-held parts of Mosul since December as part of a project by the non-profit The Institute for War and Peace Reporting (IWPR).

Penned by Iraqis across the country and gathered by volunteers, more than 2,000 letters were photocopied and showered from a transport plane.

“You will return to your most beautiful days with your family and you will hear the prayers of the mosques in Mosul sky, the culture and science will return because everything been robbed from you will come back to you,” one read.

Another said: “Our people in Mosul, we are with you in our hearts and souls, I cannot find the right words to express to you but do not forget you are part of Iraq, and we will not abandon you. Victory will come soon, God willing.”

Around 1,000 civilians crossed front lines to meet government troops on Saturday in the largest movement since fighting intensified last week but there were concerns over deteriorating humanitarian conditions for those remaining under almost constant bombardment.

An advance by Iraqi forces has slowed amid bloody resistance from jihadis, who are deploying using weaponised drones, car bombs, IEDs, sniper fire and mortars while attempting to entrench themselves in residential districts.

Special forces Lt-Gen Abdul-Wahab al-Saadi told the Associated Press that his troops were “moving very slowly” but he expected the pace to increase after Iraqi forces cut off Isis supply lines in Mosul’s south-western edge.

Iraqi forces launch push to retake western Mosul from IS

Government forces, backed by Kurdish Peshmerga fighters and international special forces from the US, UK and elsewhere, are firing shells and rockets on to Isis positions.

The US-led coalition is also launching a hail of air strikes, which Central Command said has destroyed Isis targets including mortar systems, command positions, sniper units, car bomb factories, fighting positions and a drone storage facility in recent days.

Militants have been increasing their use of weaponised drones in Iraq, dropping customised grenades and small explosives on enemy forces, vehicles and tanks before releasing footage of successful strikes on propaganda channels.

The devices have caused relatively few deaths but sparked the procurement of counter-measures after causing significant disruption to ground operations and carrying out detailed surveillance that could threaten advancing troops.

The United Nations cautioned that men, women and children inside Isis territory remain at extreme risk from the assault after finding that almost half of casualties in the military operation to retake eastern Mosul were civilians.

Over the Tigris river, the western side of the city is far more densely populated, with Isis killing anyone it finds attempting to flee.

Tom Robinson, Oxfam’s emergency team lead in Iraq, said he was “deeply concerned” for hundreds of thousands of civilians who remain trapped.

“These people have survived 30 months under Isis rule and need support to find safety, shelter and sustenance,” he added.

“We call on all armed forces to take all feasible measures to protect them.”

In pictures: Mosul offensive Show all 40 1 /40 In pictures: Mosul offensive In pictures: Mosul offensive A doctor carries an Iraqi newborn baby at a hospital in Mosul, Iraq July 18, 2017. Reuters In pictures: Mosul offensive Iraqi girls play at a yard of a school in Mosul, Iraq July 18, 2017alal Reuters In pictures: Mosul offensive A woman on crutches who is a relative of men accused of being Islamic State militants is seen at a camp in Bartella, east of Mosul, Iraq July 15, 2017. Picture taken July 15, 2017. Reuters In pictures: Mosul offensive A displaced girl, who fled from home carries a doll at Hamam al-Alil camp south of Mosul, Iraq July 13, 2017. Reuters In pictures: Mosul offensive Iraqi federal police members and civilians celebrate in the Old City of Mosul on 9 July 2017 after the government's announcement of the "liberation" of the embattled city. Iraqi Prime Minister Haider al-Abadi's office said he was in "liberated" Mosul to congratulate "the heroic fighters and the Iraqi people on the achievement of the major victory" AFP/Getty Images In pictures: Mosul offensive A picture taken on 9 July 2017, shows a general view of the destruction in Mosul's Old City. Iraq will announce imminently a final victory in the nearly nine-month offensive to retake Mosul from jihadists, a US general said Saturday, as celebrations broke out among police forces in the city. AFP In pictures: Mosul offensive Members of the Iraqi federal police raise the victory gesture as they ride on a humvee while advancing through the Old City of Mosul on 28 June 2017, as the offensive continues to retake the last district held by Islamic State (IS) group fighters. AFP/Getty Images In pictures: Mosul offensive Smoke billows as Iraqi forces advance through the Old City of Mosul on 26 June 2017, during the ongoing offensive to retake the last district held by the Islamic State (IS) group. AFP/Getty Images In pictures: Mosul offensive An Iraqi man wearing the green scarf of the Shi'ite faith kisses an Iraqi Army soldier on safely reaching the Iraqi forces position as Iraqi civilians flee the Old City of west Mosul where heavy fighting continues on 23 June 2017. Iraqi forces continue to encounter stiff resistance with improvised explosive devices, car bombs, heavy mortar fire and snipers hampering their advance. Getty Images In pictures: Mosul offensive A picture taken from the inside of an Iraqi forces armoured vehicle shows residents walking through a damaged street as troops advance towards Mosul's Old City on 18 June 2017, during the ongoing offensive to retake the last district still held by the Islamic State (IS) group. Military commanders told AFP the assault had begun at dawn after overnight air strikes by the US-led coalition backing Iraqi forces. They said the jihadists were putting up fierce resistance. AFP/Getty Images In pictures: Mosul offensive Iraqi Army soldiers advance in a destroyed street after an Iraqi forces airstrike targeted an Islamic State sniper position 17 June 2017 in al-Shifa, the last district of west Mosul under Islamic State control. IS snipers, as well as car and suicide bomb attacks continue to hinder the Iraqi forces efforts to retake the final district. A series of airstrikes by Iraqi helicopter gunships attempted to hit multiple Islamic State sniper positions in al-Shifa. Getty Images In pictures: Mosul offensive An Iraqi soldier frisks a displaced Iraqi man at a temporary camp in the compound of the closed Nineveh International Hotel in Mosul on 16 June 2017 which was recovered by Iraqi troops from Islamic State group fighters earlier in the year. A screening centre set up in the compound's fairgrounds sees a constant stream of Iraqis fleeing the battle for Mosul, awaiting their turn to be checked by the Iraqi forces who are searching for suspected Islamic State (IS) group members. The small fairground lies at the end of a pontoon bridge across the Tigris recently opened to civilians that is the only physical link between the two banks of the river. AFP/Getty Images In pictures: Mosul offensive Iraqis staying at the al-Khazir camp swim in a river near the camp for internally displaced people, located between Arbil and Mosul on 11 June 2017. AFP/Getty Images In pictures: Mosul offensive Iraqi government forces drive on a road leading to Tal Afar on 9 June 2017, during ongoing battles to retake the city from Islamic State (IS) group fighters. AFP/Getty Images In pictures: Mosul offensive An Iraqi policeman carries a poster bearing an image of Mosul's iconic leaning minaret, known as the "Hadba" (Hunchback), on 22 June 2017. AFP/Getty Images In pictures: Mosul offensive Iraqis stand in line to receive food aid in western Mosul's Zanjili neighbourhood on 7 June 2017, during ongoing battles as Iraqi forces try to retake the city from Islamic State (IS) group fighters. Living conditions in Mosul have again deteriorated since the start of the Iraqi government's offensive on the city in October in which they retook a large part of the west of the city. AFP/Getty Images In pictures: Mosul offensive Displaced Iraqis carry lightbulbs and sacks as they evacuate from western Mosul's Zanjili neighbourhood as government forces advance in the area during their ongoing battle against Islamic State (IS) group fighters on 13 May 2017 AFP/Getty Images In pictures: Mosul offensive A member of the Iraqi Counter-Terrorism Service (CTS) flashes the victory gesture as he patrols in western Mosul's al-Islah al-Zaraye neighbourhood on 13 May 2017 AFP/Getty Images In pictures: Mosul offensive Iraqi army soldiers from the 9th armoured division on a truck flash the sign of victory as they drive back from Mosul to the town of Qaraqosh (also known as Hamdaniya) Getty In pictures: Mosul offensive Members of Iraqi forces flash the sign of victory on their vehicle as they advance towards Hammam al-Alil area south of Mosul Getty In pictures: Mosul offensive A member of Iraqi security forces gestures in Hammam al-Alil, south of Mosul, Iraq Reuters In pictures: Mosul offensive Iraqi children, one flashing the sign of victory, greet Iraqi army's soldiers from the 9th armoured division in the area of Ali Rash, adjacent to the eastern Al-Intissar neighbourhood of Mosul Getty In pictures: Mosul offensive Peshmerga forces look at a tunnel used by Islamic State militants near the town of Bashiqa, east of Mosul, during an operation to attack Islamic State militants in Mosul, Iraq Reuters In pictures: Mosul offensive An Iraqi soldier takes a photograph with his phone as his comrade stands next to a detained man, whom the Iraqi army soldiers accused of being an Islamic State fighter, who was fleeing with his family in the Intisar disrict of eastern Mosul, Iraq Reuters In pictures: Mosul offensive Iranian Kurdish female members of the Freedom Party of Kurdistan (PAK) hold a position in an area near the town of Bashiqa, some 25 kilometres north east of Mosul Getty In pictures: Mosul offensive Iraqi families, who fled their homes in Hamam al-Alil, gather on the outskirts of their town Getty In pictures: Mosul offensive Displaced people walk past a checkpoint near Qayara, south of Mosul, Iraq AP In pictures: Mosul offensive Iraqi families who were displaced by the ongoing operation by Iraqi forces against jihadists of the Islamic State group to retake the city of Mosul, are seen gathering in an area near Qayyarah In pictures: Mosul offensive A boy who just fled Abu Jarbuah village is seen with his family at a Kurdish Peshmerga position between two front lines near Bashiqa, east of Mosul, Iraq Reuters In pictures: Mosul offensive An Iraqi child eats a pomegranate upon the arrival of Iraqi forces in the village of Umm Mahahir, south of Mosul Getty In pictures: Mosul offensive People who just fled Abu Jarbuah village sit as they eat at a Kurdish Peshmerga position between two front lines near Bashiqa, east of Mosul, Iraq Reuters In pictures: Mosul offensive A couple who just fled Abu Jarbuah village are escorted by Kurdish Peshmerga soldiers Reuters In pictures: Mosul offensive Women carry a boy over a wall as civilians flee their houses in the village of Tob Zawa, Iraq AP In pictures: Mosul offensive An Iraqi soldier and a civilian ride a motorbike as smoke rises behind them, on the road between Qayyarah and Mosul Getty In pictures: Mosul offensive A member of Iraqi forces, wearing a skull mask, waits at a checkpoint for people fleeing the main hub city of Mosul Getty In pictures: Mosul offensive An Iraqi soldier sits at a checkpoint in an area near Qayyarah Getty In pictures: Mosul offensive Iraqi men prepare food portions for Iraqi forces deployed in areas south of Mosul Getty In pictures: Mosul offensive Iraqi forces celebrate upon the arrival of vehicles bringing food to them Getty In pictures: Mosul offensive Iraqi childen smoke cigarettes upon the arrival of Iraqi forces in the village of Umm Mahahir, south of Mosul Getty In pictures: Mosul offensive A member of Iraqi forces distributes drinks to children in the village of Umm Mahahir, south of Mosul Getty

The International Rescue Committee said the advance on western Mosul is the operation’s “most dangerous phase” and a terrifying period for the city’s remaining residents.

Jason Kajer, the charity’s acting country director for Iraq, said: “There is a real danger that the battle will be raging around them for weeks and possibly months to come.

“More than 1,750 civilians were hurt in the fight to retake eastern Mosul and the west of the city is far more densely populated. To prevent an even greater number of civilian casualties everything must be done to keep civilians out of the firing line and as Iraqi forces reach individual neighbourhoods people must be given the opportunity to escape the city safely.”

Dozens of families gathering just beyond the front lines told journalists they were originally from villages outside the city but were forced to march inside months ago to serve as human shields for Isis fighters.

“We’ve been through terrible times,” said Juri Fathi, a mother of six who was forced to live in a school building for three months. “I had to burn my children’s clothing just for warmth.”

Iraqi forces declared eastern Mosul “fully liberated” in January after officially launching the operation to retake the city in October, but analysts have warned the battle could continue for months.

A Kurdish journalist became the latest reporter killed while covering ongoing operations, when she was fatally injured by a roadside bomb in the recently retaken town of Abu Saif.