Heavy air strikes and clashes shook the Syrian rebel enclave of Eastern Ghouta ahead of an urgent UN Security Council meeting Wednesday on the escalating violence.

The Syrian Observatory for Human Rights said 805 civilians – including at least 178 children – have been killed since Russia-backed regime forces launched an assault on the besieged enclave outside Damascus on February 18.

Russia suffered its own heavy losses on Tuesday as the defence ministry said a Russian transport plane crash landed at an airbase in western Syria, killing all 39 people on board.

Bombardment and clashes in Eastern Ghouta, the last major rebel stronghold near Damascus, have persisted despite a month-long ceasefire demanded by the Security Council more than a week ago.

At least 24 civilians were killed on Tuesday, according to the Observatory, a Britain-based monitor.

The relentless attacks prompted France and Britain to request an emergency meeting of the top UN body behind closed doors on Wednesday to discuss the ceasefire’s failure to take hold.

Government troops have advanced rapidly across farmland in Eastern Ghouta in the past week and had wrested control of 40% of the enclave as of early Tuesday.

In the enclave’s main town of Douma, air strikes have reduced homes to piles of rubble, an AFP correspondent reported.

Exhausted civil defence workers on Tuesday took advantage of a few hours of calm to dislodge the body of a resident, killed in bombardment several days ago, from a collapsed building.

Eastern Ghouta’s around 400 000 residents have lived under government siege since 2013, facing severe shortages of food and medicines even before the latest offensive began.

Forty-six aid trucks entered the area on Monday for the first time since the offensive started, but had to cut short their deliveries and leave due to heavy bombardment.

Nearly half of the food carried on the convoy could not be delivered and Syrian authorities removed some medical and health supplies from the trucks, the United Nations said.

In a statement on Tuesday UN Secretary-General Antonio Guterres said he “calls on all parties to immediately allow safe and unimpeded access for further convoys to deliver critical supplies to hundreds of thousands of people in desperate need”.

He urged all warring sides to allow aid trucks to return for a planned second delivery to Douma on Thursday.