March 20 (UPI) -- An airstrike in Eastern Ghouta Tuesday killed 15 children and two women who were in an underground school, a Syria monitor said.
Bombardment in Eastern Ghouta, with Russian air support, has so far killed at least 1,250 people. Activists said hundreds of civilians were arrested as they attempted to leave the area, adding that air raids on Monday killed at least eight civilians.
The group killed Tuesday were hiding in the school to escape government and Russian raids in the southern Syria town of Arbin, according to the Syrian Observatory for Human Rights.
The United Nations said at least 20,000 people have fled Eastern Ghouta since the bombings began several weeks ago. The 300,000 remaining in the enclave face shortages of food and medical supplies.
Assad also greeted cheering Syrian troops days earlier, after his military announced that 80 percent of the area had been retaken from anti-government forces that have held the territory since 2013.
The National Coalition for Syrian Revolutionary and Opposition Forces said the school was deliberately targeted by Russia. Moscow has previously denied carrying out airstrikes on civilians.
Monday, a letter was sent to all 15 United Nations Security Council members expressing concerns about the failure to demand a cease-fire throughout Syria. Along with the United States, the letter was signed by France, Kuwait, Sweden, Peru, Poland, Britain and the Netherlands.
Russia blocked the meeting -- with China, Kazakhstan and Bolivia -- and said the Security Council should not be discussing human rights, and should instead stick with discussions about ensuring international peace and security.
Three countries abstained from voting, which canceled the meeting due to the council's requirement of nine "yes" votes.