BEIRUT, Lebanon — An explosion at a gas station outside Damascus, the Syrian capital, on Wednesday turned a long line of cars waiting for rarely available fuel into a deadly inferno that killed at least 30 people sitting in their cars or on motorcycles, according to videos and reports from witnesses who blamed a government airstrike.

The violence came as the United Nations released a study showing that more than 60,000 people had been killed in Syria’s 22-month-old conflict, a number that is a third higher than estimates by antigovernment activist groups.

Also on Wednesday, the family of James Foley, a freelance reporter for Agence France-Presse, the Global Post Web site and other media outlets, announced that Mr. Foley had been kidnapped on Nov. 22 by unidentified gunmen in northwest Syria. Mr. Foley had survived detention by government forces in Libya while covering the conflict there.

A flurry of diplomatic activity by Russia, the United Nations’ special envoy and others aimed at finding a political solution in Syria has appeared to founder in recent days as neither Bashar al-Assad, the Syrian president, nor his opponents have expressed a willingness to make concessions to end the bloody conflict.