Wounded Syrian children are seen at a field hospital after an attacks on Jesrin town in Eastern Ghouta credit: Getty

As the fighting escalated, hundreds of pro-regime fighters were reported to have been redeployed to the front lines in Ghouta from elsewhere in Syria.

"At least 700 Afghan, Palestinian, and Syrian loyalist militiamen came from Aleppo and were sent late Tuesday to Ghouta," said Rami Abdel Rahman, head of the UK-based Syrian Observatory for Human Rights.

The offensive appears to have followed the tactics the regime and his allies have used at other key points in the war: laying siege to rebel-held areas, subjecting them to bombardment, launching a ground assault and offering passage out to civilians who flee and fighters who withdraw.

Eastern Ghouta is of particular importance due to its proximity to Assad’s seat of power in Damascus.

Some 810 civilians have been killed since the offensive started, at least 250 of which since the UN agreed a ceasefire which never came into effect.

Syrian government forces are seen in the former rebel-held area of Beit Nayem in the Eastern Ghouta region on the outskirts of the capital Damascus credit: AFP

Air strikes and mortars continued mercilessly pounding heavily populated areas of the suburb on Wednesday, leaving a further 45 dead and dozens injured.

“The situation is catastrophic,” said a doctor speaking from the rebel pocket. “Right now there is a huge escalation in Ghouta. Seventeen Russian and Syrian warplanes have been rotating in the skies, dropping cluster bomb after bomb.”

The UN humanitarian coordinator in Syria appealed to the government to commit to a ceasefire on Thursday to let in an aid convoy containing medical supplies that were stripped from a delivery on Monday.

An aid convoy reached the Damascus suburb for the first time since mid-February.

It was only the second convoy so far in 2018 to reach the area, where the UN says 400,000 residents were already running out of food and medicine even before the bombing campaign began.

Aid workers who gained access told the Telegraph they saw a destroyed town with desperate and hungry families who had been living in their basements.

Zeid al-Hussein, UN human rights chief, said the conflict had entered a "new phase of horror" and denounced claims by Syria's government that it was doing all it can to protect civilians as "frankly ridiculous".