(CNN) Syria and Russia will establish four additional humanitarian corridors into Aleppo, Russian state media reported Sunday, a day after both governments said residents had begun using the routes to flee the besieged city.

"In addition to the existing corridors, we are organizing four more humanitarian corridors," head of the Russian reconciliation center in Syria, Lt.-Gen. Sergey Chvarkov said, according to the state-run Sputnik news agency.

Syria and Russia, its key military backer, announced the creation of the three initial corridors on Thursday, after Syrian forces encircled the city and cut off rebel supply lines.

Both governments say the corridors are to allow for the distribution of badly needed food and medical aid to civilians, who have been facing a humanitarian disaster in the devastated city, and to provide residents -- along with rebels who choose to surrender -- the opportunity to leave.

The Syrian government has declared a general amnesty for rebels who surrender to government authorities within three months. The government dropped leaflets over the city last week with instructions for residents on where to find the corridors and how to approach them.

Families begin to leave, say Syria, Russia

Dozens of families began trickling out of the rebel-held neighborhoods in the east of the city on Saturday, Syrian state news agency SANA reported. They crossed into the government-controlled Salahaddin district, where Syrian army units sent them to makeshift shelters.

Syrian government leaflets dropped to the residents of besieged Aleppo.

Sputnik quoted Chvarkov as saying the existing corridors have allowed 169 civilians and 69 militants who had laid down arms to flee.

Syrian state TV showed images of what it said were women and children leaving, along a street lined with damaged buildings.

However, two sources on the ground told CNN they had visited the crossings and seen no people using them, nor any sign that they had been opened.

Meanwhile on Sunday, Syrian rebels launched an offensive to break the Aleppo siege, a member of the political leadership of Ahrar al Sham said in a video statement posted online.

Ahrar al Sham is an Islamist rebel group that is fighting Assad's army, ISIS and Kurdish forces.

Ahrar al Sham stated that all factions in the Islamist umbrella group Jaish al Fatah would take part in the battle across the 20 kilometer front line.

Witnesses told CNN they have seen an increase in artillery fire and rocket activity near the front lines. Many residents started fires hoping the smoke would obscure the vision of pilots flying overhead, witnesses on the ground said.

Aleppo, Syria's largest city before the war broke out in 2011 and the country's economic hub, has been a major battleground in the conflict, with rebel groups holding neighborhoods in the east of the city for years. They include so-called moderate factions such as the Free Syrian Army, as well as various Islamist groups, including those, such as Jabhat al-Nusra, that have been designated terrorist organizations.

Photos: Syria's civil war, in pictures Displaced Syrian residents wait to receive food aid distributed by the UN Relief and Works Agency at the besieged al-Yarmouk camp, south of Damascus, Syria, on January 31, 2014. According to the UN Envoy for Syria, an estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. See how the conflict has unfolded. Hide Caption 1 of 52 Photos: Syria's civil war, in pictures Hide Caption 2 of 52 Photos: Syria's civil war, in pictures An injured man lying in the back of a vehicle is rushed to a hospital in Daraa, Syria, on March 23, 2011. Violence flared in Daraa after a group of teens and children were arrested for writing political graffiti. Dozens of people were killed when security forces cracked down on demonstrations. Hide Caption 3 of 52 Photos: Syria's civil war, in pictures Anti-government protesters demonstrate in Daraa on March 23, 2011. In response to continuing protests, the Syrian government announced several plans to appease citizens. Hide Caption 4 of 52 Photos: Syria's civil war, in pictures Syrian children walk over bricks stored for road repairs during a spontaneous protest June 15, 2011, at a refugee camp near the Syrian border in Yayladagi, Turkey. Hide Caption 5 of 52 Photos: Syria's civil war, in pictures Jamal al-Wadi speaks in Istanbul on September 15, 2011, after an alignment of Syrian opposition leaders announced the creation of a Syrian National Council -- their bid to present a united front against Bashar al-Assad's regime and establish a democratic system. Hide Caption 6 of 52 Photos: Syria's civil war, in pictures Delegates from Arab League member states and Turkey discuss a response to the government's crackdown in Syria on November 16, 2011. Hide Caption 7 of 52 Photos: Syria's civil war, in pictures Supporters of al-Assad celebrate during a referendum vote in Damascus on February 26, 2012. Opposition activists reported at least 55 deaths across the country as Syrians headed to the polls. Analysts and protesters widely described the constitutional referendum as a farce. "Essentially, what (al-Assad's) done here is put a piece of paper that he controls to a vote that he controls so that he can try and maintain control," a US State Department spokeswoman said. Hide Caption 8 of 52 Photos: Syria's civil war, in pictures Syrian refugees walk across a field in Syria before crossing into Turkey on March 14, 2012. Hide Caption 9 of 52 Photos: Syria's civil war, in pictures Rebel fighters with the Free Syrian Army capture a police officer in Aleppo, Syria, who they believed to be pro-regime militiaman on July 31, 2012. Dozens of officers were reportedly killed as rebels seized police stations in the city. Hide Caption 10 of 52 Photos: Syria's civil war, in pictures A Free Syrian Army fighter runs for cover as a Syrian Army tank shell hits a building across the street during clashes in the Salaheddine neighborhood of central Aleppo on August 17, 2012. Hide Caption 11 of 52 Photos: Syria's civil war, in pictures Family members mourn the deaths of their relatives in front of a field hospital in Aleppo on August 21, 2012. Hide Caption 12 of 52 Photos: Syria's civil war, in pictures A Syrian man carrying grocery bags dodges sniper fire in Aleppo as he runs through an alley near a checkpoint manned by the Free Syrian Army on September 14, 2012. Hide Caption 13 of 52 Photos: Syria's civil war, in pictures Free Syrian Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16, 2012. Hide Caption 14 of 52 Photos: Syria's civil war, in pictures Smoke rises over the streets after a mortar bomb from Syria landed in the Turkish border village of Akcakale on October 3, 2012. Five people were killed. In response, Turkey fired on Syrian targets and its parliament authorized a resolution giving the government permission to deploy soldiers to foreign countries. Hide Caption 15 of 52 Photos: Syria's civil war, in pictures A Syrian rebel walks inside a burnt section of the Umayyad Mosque in Aleppo hours before the Syrian army retook control of the complex on October 14, 2012. Hide Caption 16 of 52 Photos: Syria's civil war, in pictures An Israeli tank crew sits on the Golan Heights overlooking the Syrian village of Breqa on November 6, 2012. Israel fired warning shots toward Syria after a mortar shell hit an Israeli military post. It was the first time Israel fired on Syria across the Golan Heights since the 1973 Yom Kippur War. Hide Caption 17 of 52 Photos: Syria's civil war, in pictures Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo as fighting continues through the night on December 1, 2012. Hide Caption 18 of 52 Photos: Syria's civil war, in pictures The bodies of three children are laid out for identification by family members at a makeshift hospital in Aleppo on December 2, 2012. The children were allegedly killed in a mortar shell attack that landed close to a bakery in the city. Hide Caption 19 of 52 Photos: Syria's civil war, in pictures A father reacts after the deaths of two of his children in Aleppo on January 3, 2013. Hide Caption 20 of 52 Photos: Syria's civil war, in pictures Syrians look for survivors amid the rubble of a building targeted by a missile in the al-Mashhad neighborhood of Aleppo on January 7, 2013. Hide Caption 21 of 52 Photos: Syria's civil war, in pictures Rebels launch a missile near the Abu Baker brigade in Al-Bab, Syria, on January 16, 2013. Hide Caption 22 of 52 Photos: Syria's civil war, in pictures An aerial view shows the Zaatari refugee camp near the Jordanian city of Mafraq on July 18, 2013. Hide Caption 23 of 52 Photos: Syria's civil war, in pictures The UN Security Council passes a resolution September 27, 2013, requiring Syria to eliminate its arsenal of chemical weapons. Al-Assad said he would abide by the resolution. Hide Caption 24 of 52 Photos: Syria's civil war, in pictures Residents run from a fire at a gasoline and oil shop in Aleppo's Bustan Al-Qasr neighborhood on October 20, 2013. Witnesses said the fire was caused by a bullet from a pro-government sniper. Hide Caption 25 of 52 Photos: Syria's civil war, in pictures Syrian children wait as doctors perform medical checkups at a refugee center in Sofia, Bulgaria, on October 26, 2013. Hide Caption 26 of 52 Photos: Syria's civil war, in pictures An injured man is helped following an airstrike in Aleppo's Maadi neighborhood on December 17, 2013. Hide Caption 27 of 52 Photos: Syria's civil war, in pictures A man holds a baby who was rescued from rubble after an airstrike in Aleppo on February 14, 2014. Hide Caption 28 of 52 Photos: Syria's civil war, in pictures A US ship staff member wears personal protective equipment at a naval airbase in Rota, Spain, on April 10, 2014. A former container vessel was fitted out with at least $10 million of gear to let it take on about 560 metric tons of Syria's most dangerous chemical agents and sail them out to sea, officials said. Hide Caption 29 of 52 Photos: Syria's civil war, in pictures A Free Syrian Army fighter fires a rocket-propelled grenade during heavy clashes in Aleppo on April 27, 2014. Hide Caption 30 of 52 Photos: Syria's civil war, in pictures A giant poster of al-Assad is seen in Damascus on May 31, 2014, ahead of the country's presidential elections. He received 88.7% of the vote in the country's first election after the civil war broke out. Hide Caption 31 of 52 Photos: Syria's civil war, in pictures Rebel fighters execute two men on July 25, 2014, in Binnish, Syria. The men were reportedly charged by an Islamic religious court with detonating several car bombs. Hide Caption 32 of 52 Photos: Syria's civil war, in pictures Photographs of victims of the Assad regime are displayed as a Syrian army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The July 31, 2014, briefing was called "Assad's Killing Machine Exposed: Implications for U.S. Policy." Caesar, apparently a witness to the regime's brutality, smuggled more than 50,000 photographs depicting the torture and execution of more than 10,000 dissidents. CNN cannot independently confirm the authenticity of the photos, documents and testimony referenced in the report. Hide Caption 33 of 52 Photos: Syria's civil war, in pictures Volunteers remove a dead body from under debris after shelling in Aleppo on August 29, 2014. According to the Syrian Civil Defense, barrel bombs are now the greatest killer of civilians in many parts of Syria. The White Helmets are a humanitarian organization that tries to save lives and offer relief. Hide Caption 34 of 52 Photos: Syria's civil war, in pictures Medics tend to a man's injuries at a field hospital in Douma after airstrikes on September 20, 2014. Hide Caption 35 of 52 Photos: Syria's civil war, in pictures A long-exposure photograph shows a rocket being launched in Aleppo on October 5, 2014. Hide Caption 36 of 52 Photos: Syria's civil war, in pictures Rebel fighters dig caves in the mountains for bomb shelters in the northern countryside of Hama on March 9, 2015. Hide Caption 37 of 52 Photos: Syria's civil war, in pictures Nusra Front fighters inspect a helicopter belonging to pro-government forces after it crashed in the rebel-held Idlib countryside on March 22, 2015. Hide Caption 38 of 52 Photos: Syria's civil war, in pictures A Syrian child fleeing the war gets lifted over fences to enter Turkish territory illegally near a border crossing at Akcakale, Turkey, on June 14, 2015. Hide Caption 39 of 52 Photos: Syria's civil war, in pictures A refugee carries mattresses as he re-enters Syria from Turkey on June 22, 2015, after Kurdish People's Protection Units regained control of the area around Tal Abyad, Syria, from ISIS. Hide Caption 40 of 52 Photos: Syria's civil war, in pictures A sandstorm blows over damaged buildings in the rebel-held area of Douma, east of Damascus, on September 7, 2015. Hide Caption 41 of 52 Photos: Syria's civil war, in pictures Members of a Syrian opposition group attack the headquarters of al-Assad regime forces in the Aleppo villages of Nubul and al-Zahraa on February 12, 2016. Hide Caption 42 of 52 Photos: Syria's civil war, in pictures This still image, taken from a video posted by the Aleppo Media Center, shows a young boy in an ambulance after an airstrike in Aleppo, Syria, on August 17, 2016. It took nearly an hour to dig the boy, identified as Omran Daqneesh, out from the rubble, an activist told CNN. The airstrike destroyed his home, where he lived with his parents and two siblings. Director of the Aleppo Media Center Yousef Saddiq said Omran's 10-year-old brother, Ali, died from his injuries. Hide Caption 43 of 52 Photos: Syria's civil war, in pictures Smoke rises after an airstrike in Aleppo on October 4, 2016. Hide Caption 44 of 52 Photos: Syria's civil war, in pictures Arabic writing that reads "some day we will return" is seen on a bus window as civilians evacuate Aleppo on December 15, 2016. The evacuations began under a new ceasefire between rebels and pro-government forces. Hide Caption 45 of 52 Photos: Syria's civil war, in pictures This photo, provided by the activist Idlib Media Center, shows dead children after a suspected chemical attack in the rebel-held city of Khan Sheikhoun on April 4, 2017. Dozens of people were killed, according to multiple activist groups. The United States responded a few days later by launching between 50-60 Tomahawk missiles at a Syrian government airbase. US officials said the base was home to warplanes that carried out the chemical attack. Syria has repeatedly denied it had anything to do with the attack. Hide Caption 46 of 52 Photos: Syria's civil war, in pictures Members of the UN Security Council raise their hands on April 12, 2017, as they vote in favor of a draft resolution that condemned the reported use of chemical weapons in Syria. Hide Caption 47 of 52 Photos: Syria's civil war, in pictures Residents of the war-torn city of Douma break their Ramadan fast on June 18, 2017. Hide Caption 48 of 52 Photos: Syria's civil war, in pictures A member of the Syrian pro-regime forces fires a machine gun as a comrade holds his feeding ammunition belt on November 11, 2017. It was during an advance toward rebel-held positions west of Aleppo. Hide Caption 49 of 52 Photos: Syria's civil war, in pictures A child receives medical treatment after a village was attacked in the rebel-held Eastern Ghouta region on February 25, 2018. Several people were treated for exposure to chlorine gas, opposition groups said, as airstrikes and artillery fire from the regime continued. CNN was unable to independently verify claims that chlorine was used as a weapon. Hide Caption 50 of 52 Photos: Syria's civil war, in pictures Bodies lie on the ground in the rebel-held city of Douma, Syria, on April 8, 2018. According to activist groups, helicopters dropped barrel bombs filled with toxic gas on Douma, which has been the focus of a renewed government offensive that launched in mid-February. The Syrian government and its key ally, Russia, vehemently denied involvement and accused rebel groups of fabricating the attack to hinder the army's advances and provoke international military intervention. Hide Caption 51 of 52 Photos: Syria's civil war, in pictures Damascus skies erupt with anti-aircraft fire as the US and its allies launch an attack on Syria's capital early on April 14, 2018. US President Donald Trump announced airstrikes in retaliation for Syria's alleged use of chemical weapons. Trump says the strikes are part of a sustained military response, in coordination with France and the United Kingdom. Hide Caption 52 of 52

Residents describe life under siege

The United Nations has warned of a potential humanitarian catastrophe in Aleppo as regime troops, backed by Russian air power, tighten their grip on the ruined city. An estimated 200,000 to 300,000 people remain in the besieged rebel-held part of eastern Aleppo.

In addition to the continual bombardment they face, which has seen numerous hospitals struck, residents complain of acute shortages of food, water and medicine.

"Markets are empty of vegetables and all other food products, streets are empty of cars and vehicles because there is no fuel," an aid organization manager based in Aleppo told CNN Sunday, as bombs continued to pound rebel-held neighborhoods.

He said the shortages had forced his organization to resort to reusing "single-use" medical equipment after attempting to sterilize it.

An emergency responder in Aleppo confirmed to CNN that rebel-held neighborhoods were under aerial bombardment from Russian jets Sunday. Ambulances and other emergency vehicles in the city were out of fuel, he said.

The United Nations' special envoy for Syria, Staffan de Mistura, has said that food supplies in rebel-held areas could run out within weeks.

Russia: Aid is ready for fleeing residents

Russia says that it has prepared 14 tons of humanitarian cargo for those who leave the city, with 2.5 tons of food and other essentials already supplied.

But some residents contacted by CNN say they are wary of the government's promise they will be safe if they leave the rebel-held areas.

The corridors also have been regarded with skepticism by international actors.

JUST WATCHED Aid workers: Situation is desperate in eastern Aleppo Replay More Videos ... MUST WATCH Aid workers: Situation is desperate in eastern Aleppo 02:36

U.S. Secretary of State John Kerry suggested Friday that the corridor approach could potentially be a "ruse," telling reporters that it carried "the risk, if it is a ruse, of completely breaking apart the level of cooperation" between the United States and Russia.

However, he said, "if we're able to work it out ... and have a complete understanding of what is happening and then agreement on the way forward, it could actually open up some possibilities."

De Mistura says introducing such measures should be left to the U.N. and its partners, and has stressed that no one should be forced to leave.

And Amnesty International has questioned whether the corridors will help prevent a humanitarian disaster, saying many residents are unlikely to trust government assurances over their safety.

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U.S.-backed force recaptures 40% of city of Manbij

Elsewhere in Syria, thousands of civilians have also fled ISIS-held parts of the northern city of Manbij, some 80 kilometers (50 miles) northeast of Aleppo, over the past day, the UK-based Syrian Observatory for Human Rights reported Sunday.

Backed by the air power of the U.S.-led coalition, the alliance of U.S.-backed Kurdish and Arab forces -- known as the Syrian Democratic Forces -- has been engaged in fierce clashes with the Sunni terror group in the city.

The SDF had recaptured about 40% of the city from ISIS as of Sunday, the UK-based monitoring group reported.

U.S. officials describe Manbij as a strategic supply point for ISIS, and the terror group's principal hub between Raqqa, the capital of its self-declared caliphate, and Turkey.

Clashes are still ongoing with ISIS militants in several other parts of the city, the observatory said.

More than 280,000 Syrians have been killed since fighting began in 2011, and millions have been forced to flee the country.