Civilians breathe through an oxygen mask at al-Quds hospital, after a hospital and a civil defence group said a gas, what they believed to be chlorine, was dropped alongside barrel bombs on a neighbourhood of the Syrian city of Aleppo, Syria, early August 11, 2016.Reuters

Fifteen of the last 35 doctors left in the Syrian city of Aleppo have appealed to US President Barack Obama to put a stop to the airstrikes on hospitals in the rebel-held city and provide assistance to the 250,000 civilians trapped in the area.

"We do not need tears or sympathy or even prayers: we desperately need a zone free from bombing over eastern Aleppo to stop the attacks, and international action to ensure Aleppo is never besieged again," the doctors wrote in a letter signed by them, adding that if attacks on hospitals and other medical facilities continued, there would be nothing left within a month.

The Russians have said that they would halt military action in the besieged city for three hours a day to allow medical aid to come into Aleppo, the Guardian reported.

At least one medical facility is being attacked every 17 hours, according to media reports. Doctors are left with no option but to make drastic decisions and let children die due to the lack of medical supplies, blood and scanners.

Since the uprising against Syrian President Bashar al-Assad, doctors have "borne witness as countless patients, friends and colleagues suffered violent, tormented deaths... The world has stood by and remarked how 'complicated' Syria is, while doing little to protect us. Recent offers of evacuation from the regime and Russia have sounded like thinly veiled threats to residents - flee now or face what fate?" doctors said in the letter to Obama.

"Two weeks ago, four newborn babies gasping for air suffocated to death after a blast cut the oxygen supply to their incubators. Gasping for air, their lives ended before they had really begun," they added.

Doctors have said that there have been 42 attacks on medical facilities in Syria in one month. Fifteen out of those 42 attacks have been on hospitals where they work.

"Continued US inaction to protect the civilians of Syria means that our plight is being wilfully tolerated by those in the international corridors of power. The burden of responsibility for the crimes of the Syrian government and its Russian ally must therefore be shared by those, including the United States, who allow them to continue," the doctors warned Obama, the BBC reported.

They added that "it will be only a matter of time until we are again surrounded by regime troops, hunger takes hold and hospitals' supplies run completely dry if a permanent lifeline to Aleppo was not immediately opened."

Stephen O'Brien, UN humanitarian chief, was quoted by the Guardian as saying that he was willing to consider the Russian plan. However, at least a 48-hour pause in the fighting and an open single-carriageway road would be required to get enough medical aid into the city.

"When we're offered three hours, then you have to ask: what could be achieved in those three hours? Is it to meet the need or will it only just meet a very small part of the need?" O'Brien said.

The doctors, while appealing to the American President to put an end to the bombardment of medical facilities, said in the letter: "Prove that you are the friend of Syrians."