The most senior civic leader in the besieged Syrian city of Aleppo has condemned the west for failing to stop Russian airstrikes cutting off the city and warned of a disastrous humanitarian crisis within weeks.

A fortnight after President Bashar al-Assad’s forces, with Russian air support, cut the only road into rebel-held Aleppo, it is claimed a water shortage is affecting hospitals. Brita Haji Hasan, leader of the Aleppo city council, said that the situation was deteriorating rapidly and that he believed the rebel-held areas could only hold out for “two to three months” before people started to die in their thousands.

“We have reserves, stores, but Aleppo is home to 326,000 people who are besieged,” Haji Hasan said. “It is not a small city, it is an industrial city. We can keep going for two to three months, but then people will starve in large numbers. We are facing a major humanitarian crisis and nobody is helping us. Everyone is just watching. Most of the civilians already dying now are women and children.”

We can keep going for two to three months, but then people will starve in large numbers Brita Haji Hasan

The head of delegation for the International Committee of the Red Cross (ICRC) in Syria, Marianne Gasser, told the Observer that the situation was already critical in Aleppo’s remaining hospitals.

She said: “Numerous health facilities have been attacked and are now out of service, depriving many more of lifesaving medical care. There is no more respect for hospitals and medical staff.

“The lack of electricity and water is also mainly affecting hospitals.”

She added: “This week one doctor told me: ‘Doctors and nurses used to rotate with other physicians. But now it is almost impossible to have any relief. Some days we receive dozens of emergency cases. We are all exhausted and desperate, but I refuse to abandon my post. I want to care for the Syrian people from all over Aleppo and beyond. It is my duty and obligation to help and care for all those in need’.”

The Castello road, the last rebel artery north towards the Turkish border, was bombed 250 times over a fortnight ago in a major barrage which allowed fighters to cut off Aleppo.

The Russian airstrikes have continued to hit the road, said Haji Hasan, speaking from the Turkish border city of Gaziantep, where he was recovering from injuries sustained in a mortar attack.

He claimed that in two days last week there had been another 100 missile strikes on the Castello road and that Russian jets had then moved on to attack civilian sites in the city before flying back to their bases.Haji Hasan said the US and the west had a duty to engage with the crisis in Aleppo. “All we need is for the Russian airstrikes to stop,” he said. “The [moderate] Syrian Free Army will then be able to take back the Castello road. That is all we need.

“The regime is using starvation as a weapon and the west does not seem bothered by it. Our food and water is not going to last. There is so much destruction from the Russians – the attacks are non-stop.

“And they are using everything: cluster bombs, barrel bombs, phosphorous bombs and even new weapons we have not seen before. They are not killing fighters. They are killing civilians.”

Gasser, who is currently in Aleppo, said that many in the city had now reached the limits of their endurance.

“There are tens of thousands of displaced and vulnerable people with no income and no savings,” she said. “They struggle to meet their needs for food, water, healthcare and other basic services.

“People we meet who are displaced took shelter in schools, in unfinished buildings and other facilities, some of which are simply skeleton infrastructure. Most people with whom I spoke have been displaced for at least two to three years.

“Many of them see no prospect of returning home any time soon, either because fighting is still going on, or because for many of them, their homes and land have been damaged, burned or destroyed.

“Every single family is affected, and most communities in Aleppo, and beyond, have reached the limit of their endurance.”

Aid workers have said there is just enough fuel to keep generators, bakeries,and hospitals running for a month. On 13 July, the United Nations Office for the Coordination of Humanitarian Affairs (Ocha) released a statement saying the UN only had food supplies for only 145,000 people for a month.

Rebel forces entered Aleppo in 2012, dividing it between opposition areas in the east and government-controlled ones in the west. However, the rebel-held areas have been almost surrounded since February by pro-government militants backed by Russian warplanes, which have tipped the balance in favour of Assad’s forces.