WASHINGTON: The U.S. Thursday blacklisted 18 senior Syrian officials it said were connected to the country’s weapons of mass destruction program, after an international investigation found Syrian government forces were responsible for chlorine gas attacks against civilians.

The action marked the first time the U.S. has sanctioned Syrian military officials for the government’s use of chemical weapons, according to a Treasury Department statement.

Meanwhile, the U.N.’s Syria envoy said meetings were taking place in Ankara and Moscow to avert a dangerous military escalation and help end the water crisis affecting millions in Damascus and its suburbs.

In the city itself, a suicide bomber killed at least eight people in the upscale, heavily policed neighborhood of Kafr Souseh, Syrian state TV reported. The target of the attack was not immediately known.

Part of Kafr Souseh is a restricted zone that is home to ministers, senior security officials and intelligence headquarters, but the explosion happened away from that area.

Earlier Thursday, opposition activists reported a mounting number of government airstrikes, including a raid in the northern Aleppo province that killed at least six civilians.

The opposition-run Syrian civil defense said its workers pulled the bodies of three children and three adults from the rubble of an airstrike on the village of Babka in the opposition-held countryside west of Aleppo. It was not clear who was behind the raid and others like it in the Aleppo countryside.

Syrian and Russian aircraft regularly bombed the province before the cease-fire went into effect. The U.S. is believed to be behind a series of strikes in the neighboring Idlib province that activists say have killed several Al-Qaeda-linked militants.

The raid followed a day of strikes on two rebel pockets outside Damascus. The strikes on the Ghouta region, where pro-government forces are waging a ground offensive against rebels, were the first since the nearly two-week old cease-fire came into effect, according to the Britain-based Syrian Observatory for Human Rights.It is not clear how the ongoing violence may affect talks, sponsored by Russia and Turkey, expected on Jan. 23 in Astana, Kazakhstan. Little is clear about what is on the agenda of the negotiations or who will be attending.

In Geneva, Staffan de Mistura said he was concerned that fighting northwest of Damascus that has cut off the capital’s clean water supply would further escalate and derail negotiations in Astana. He said five villages in the Wadi Barada area had reached an “arrangement” with the government, but two villages, including one which holds the source of water, Ain Fijeh, have not. The leader of one of Syria’s largest rebel factions, Ahrar al-Sham, said in remarks aired Thursday that the violence in the valley and daily airstrikes on rebel-held areas “are signs of a collapsing truce.”

A joint inquiry by the U.N. and the Organization for the Prohibition of Chemical Weapons found Syrian government forces were responsible for three chlorine gas attacks and that Daesh (ISIS) militants had used mustard gas, according to reports seen by Reuters in August and October.

Following the reports of the international inquiry, Britain and France circulated a draft resolution to the U.N. Security Council in December that would ban the sale or supply of helicopters to the Syrian government and blacklist 11 Syrian military commanders and officials over chemical weapons attacks during the nearly 6-year-old war. A vote on the draft resolution has not yet been set, but diplomats said Russia, one of five council veto powers, has made clear it opposed the measures.