Mahdi Mirza, director of communications for the Syrian American Medical Society, said: ‘We have a problem… We need to get our house in order to avoid the tragedy that has engulfed us.’ ‘We have no option. All the medical and other facilities in the area have shut down as medical aid has run out.’ Meanwhile, the Free Syrian Army said rebel groups had cut off some of the busiest roads heading into Syria from Turkey.

Al-Majalah, the first big hospital to be overrun, received 800 wounded, including 200 soldiers and a large number of civilians, according to activists in the local region.

‘There are just no more places left where you can go for medical treatment,’ Dr Zahi Khaled, an opposition activist, told the Associated Press.

Hundreds more injured were being treated in the nearby Bab al-Hawa district, east of the city.

It is the biggest single massacre so far in Syria, where the government and its backers have largely given up efforts to crush a rebellion that began as peaceful protests.

On Tuesday, US President Barack Obama vowed additional US support for Syrian rebels.

However, he also pledged that any strikes targeting Syria’s government forces would be part of an international coalition.

President Bashar al-Assad blames the crisis on a conspiracy by Saudi Arabia in a war on Sunni Muslims.

‘Our role is to protect our nation in its time of need and give it dignity,’ Mr Obama said in a statement.

‘We are also prepared to do our part within a global coalition to stop chemical weapons use and support the government of the Syrian people.’

Russia had offered to lead a new international meeting to discuss the crisis involving 15 major powers, including the US – to discuss any possible action, Kremlin officials said on Monday.

The UN says at least 9,500 have been killed in Syria since March 2011, with hundreds of thousands more detained or driven from their homes.

In another attempt to bring peace back to rebel-held areas, Syrian rebels said they had seized control of villages around Qaboun, a town about 20 miles southwest of Damascus which were also seized by rebels last month.

The rebels said troops had been ordered not to enter the towns, which include some of the oldest Christian communities in Syria.

They said the offensive did not threaten the town, which is protected by the Lebanese Shia group Hezbollah who are present nearby