BEIRUT, Lebanon — Hundreds of people were allowed to leave a besieged, rebel-held suburb of Damascus, the Syrian capital, on Sunday in a rare cease-fire, according to the government and its opponents. But aid workers said they were still unable to enter the town, Moadhamiyeh, which international organizations have been trying to reach for months and where six people have reportedly died of malnutrition.

Further underscoring the challenges of providing humanitarian aid in Syria, where millions are displaced and needy, seven aid workers were abducted near the town of Saraqeb in the northern province of Idlib on Saturday.

Six were staff members at the International Committee of the Red Cross, aid officials said, and one was a volunteer at the Red Cross’s local affiliate, the Syrian Arab Red Crescent. Officials declined to give the victims’ nationalities.

Kidnapping is a growing problem in rebel-held areas of northern Syria, where there is infighting among rebel factions and where jihadist organizations hostile to Western aid groups and Syrian civil activists are on the rise, along with criminal gangs seeking to profit from ransom.