Western powers turned up the heat on Damascus on Friday (March 2nd) as tens of thousands of civilians in Syria's battered opposition enclave of Eastern Ghouta awaited desperately needed aid, AFP reported.

More than 600 civilians have been killed in the enclave outside Damascus since Syrian regime forces launched an assault on February 18th.

Eastern Ghouta's 400,000 residents have lived under siege since 2013, facing severe food and medicine shortages even before the latest offensive.

The UN Human Rights Council was to hold an emergency session later Friday on the crisis, as dozens of aid trucks remained unable to enter the enclave.

The US, Germany and France upped the pressure on Damascus after a UN Security Council demand for a ceasefire failed to stem the fighting.

US President Donald Trump and German Chancellor Angela Merkel agreed in a phone call that the Syrian regime must be held accountable.

"This applies both to the Assad regime's deployment of chemical weapons and for its attacks against civilians and the blockade of humanitarian support," a German chancellery statement said.

Trump and French President Emmanuel Macron, meanwhile, vowed there would be "no impunity" in the event of further chemical weapons use in Syria.

On Friday, distrust ran high among civilians in Eastern Ghouta on the fourth day of a daily five-hour "humanitarian pause".

The pause announced by Russia has tempered but not halted the bombing, which has ripped through houses and reduced residential areas to rubble.

Embattled Syrian civilians have not left the enclave, despite a Russian offer of safe passage out during the daily halt in fighting.

Early Friday, before the pause, warplanes pounded areas including Douma and the town of Zamalka, the Syrian Observatory for Human Rights said.

Rockets fell on Douma and Harasta during the pause, the monitor said, as regime forces advanced on the southern outskirts of the enclave.

On Thursday, Jan Egeland, head of the UN's humanitarian taskforce for Syria, said he hoped aid convoys may be able to go to Eastern Ghouta "in the next few days".