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.”

Videos that activist groups said showed the aftermath of the air defense base attack raised the possibility that rebels had captured shoulder-fired antiaircraft missiles, known as Manpads, but it was unclear whether some had the components to make them functional. One video, uploaded on Friday, appeared to show a man holding a complete system.

Rebel groups have been eager to acquire the weapons to counter the government’s increasing use of warplanes and helicopters. There have been several recent sightings of Manpads, possibly smuggled from abroad or seized in raids on government arsenals.

That seemed likely to raise concerns about the spread of the weapons, which can also be used against commercial airliners.

The videos from the air defense base, in Al Bukamel, near Syria’s border with Iraq, could not be independently verified. They showed rebel fighters strolling through a darkened building, with the bodies of at least two government soldiers lying on the ground.

One of the dead soldiers is covered in what looks like ash. Soldiers stand over another body, caked in blood, as someone pokes the dead man’s head with a rifle. After the capture of the base, antigovernment groups said that several people were killed when government warplanes attacked the area, raising questions about the rebels’ ability to hold the site.

Also on Saturday, Syria’s state news agency said that the government had released more than 300 people detained during recent fighting in the Damascus suburbs, Homs, Aleppo and Dara’a. The news agency said the detainees had been “involved in recent events,” but had committed no crimes.

A reporter with Agence France-Presse who interviewed some detainees as they emerged from a Damascus police station said several appeared to have been beaten. Some left the station wearing nothing but underwear and others were shoeless. One detainee said that he had spent 32 days in solitary confinement for having a damaged identity card.

In recent days, activists and international filmmakers have expressed concern about the fate of Orwa Nyrabia, a leading figure in Syrian cinema believed to have been arrested at the Damascus airport on Aug. 23. Mr. Nyrabia, founder and artistic director of the Damascus Dox Box Film Festival, had been en route to Cairo, said Mohammad al-Attar, a Syrian playwright and friend.

“He has left the country many times before, for short trips,” Mr. Attar said. “For me there was no clear reason” for the government to arrest Mr. Nyrabia. “They have their own plans. You never know when it’s the time.”

NY Times