Syrian regime forces have seized on Sunday about a quarter of the Damascus eastern Ghouta where forces loyal to head of the regime launched last February 27 one of the most ferocious assaults of Syria’s civil war, including airstrikes and rocket and artillery bombardment that killed hundreds of civilians. The advances into the last major rebel enclave near the capital have forced thousands of civilians to flee deeper into the rebel-held territory, where some 400,000 people live, the Syrian Observatory for Human Rights and a resident told Reuters on Sunday. A main insurgent group in eastern Ghouta, Jaysh al-Islam, said the regime “scorched earth policy” had forced rebels to retreat and regroup. In its first official comment on developments in eastern Ghouta, Syrias SANA news agency quoted a military source as saying that Syrian regime forces “advanced on several fronts and retook control of several farms and villages.” Separately, a UN humanitarian official said people in eastern Ghouta were being subjected to unacceptable “collective punishment”, which is illegal under the Geneva Conventions. The official called on implementing the 30-day countrywide ceasefire demanded by the UN Security Council. In London, Prime Minister Theresa May held a phone call with US President Donald Trump and both sides agreed that the "overwhelming responsibility" for the "humanitarian catastrophe" in eastern Ghouta fell on the Syrian regime and Russia, May’s office said. UN Regional Humanitarian Coordinator for the Syria Crisis, Panos Moumtzis said in a statement on Sunday that about 600 people have been killed in Syrias eastern Ghouta since February 18 and over 2,000 have been injured. “At the same time, ground-based strikes and mortar shelling from eastern Ghouta have killed and injured scores of civilians in neighboring Damascus," Moumtzis said. Earlier, a UN official in Syria told Reuters a humanitarian convoy carrying life-saving supplies would not enter eastern Ghouta as had been planned on Sunday, citing a lack of permission.