BEIRUT, Lebanon — Opposition fighters in Syria said early Saturday that they had captured an air defense base in the eastern province of Deir el-Zour, taking at least 16 soldiers captive and seizing weapons and ammunition in what appeared to be part of a broader rebel offensive against Syrian military installations in several parts of the country.

Rebel fighters in the province also attacked a military air base, according to activist groups, the third attack on an air force site in the past few days. Last week, rebel commanders claimed to have destroyed several helicopters during attacks on two separate military airports in the northern Idlib Province.

The latest attacks came as the new Syria representative for the United Nations and Arab League, seeking to revive stalemated diplomacy, said he would travel to Damascus in the coming days. The representative, Lakhdar Brahimi, a veteran Algerian diplomat, also said he intended to base himself in Damascus if that would be more useful.

“Damascus is the right, natural place to be,” Mr. Brahimi said in an interview at the United Nations during his first official day on the job. “Whether it will be possible or not is something I’m going to find out.”