BEIRUT — The UN reached thousands of beleaguered Syrians with emergency food relief for the first time in more than a month on Monday, amid warnings that conditions outside the Syrian capital of Damascus have deteriorated to desperate levels under a suffocating government blockade.

The UN’s humanitarian agency, the World Food Program, and the Syrian Arab Red Crescent announced that they were able to reach the eastern Ghouta suburbs of Damascus with enough food for 40,000 people.

The supplies cover only a fraction of the estimated 350,000 people in need in the eastern Ghouta region, according to UN figures. It is one of the last remaining pockets of opposition to Syrian President Bashar Assad and depends on relief and smuggling to survive an enduring government siege.

The Syrian Arab Red Crescent, which operates across conflict lines, also said it had completed its measles vaccination campaign in eastern Ghouta, vaccinating 48,000 children over two drives, in May and October.

Photos of children gaunt with hunger in eastern Ghouta shocked observers last week, and UN High Commissioner for Human Rights Zeid Ra’ad Al Hussein called the siege ‘‘an outrage.’’

‘‘The people here do not want assistance; they want someone to break the blockade and stop the shelling. The relief we’ve received will not last for even a few days,’’ said local activist Anas al-Dimashqi.

The delivery coincided with the resumption of talks between the government, rebels, and their international sponsors Russia, Turkey, and Iran.

Associated Press