BEIRUT — 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 prisoner and seizing weapons and ammunition. The action appeared to be part of a broader rebel offensive against Syrian military installations across the country.
Activist groups said rebel fighters in the province also attacked a military air base, the third attack on an air force site in recent days.
Meanwhile, the United Nations' new envoy to Syria told President Bashar Assad's regime that change is both "urgent" and "necessary" and that it must meet the "legitimate" demands of the Syrian people. His words will not win the seasoned Algerian diplomat and international troubleshooter any friends in Damascus.
On his first day on the job, Lakhdar Brahimi also called on both sides to end violence in Syria but said Assad's government bears more responsibility than anyone else to halt the bloodshed. These remarks were seemingly intended to push the Damascus government to ease off military operations to create a better atmosphere for his peace mission.
"I call on parties inside Syria to halt the fighting. Undoubtedly, this call is primarily directed to the government. More than others, it is the duty of governments, under any circumstances and anywhere, not just in Syria, to ensure security and stability for their people," Mr. Brahimi told al-Arabiya television in an interview from New York.
The Syrian government had no immediate response to the comments made by Mr. Brahimi, who replaced Kofi Annan, who quit after his six-point plan including an April 12 cease-fire failed to stop the Syrian civil war.
Mr. Brahimi made his comments as the battle for control of Syria's largest city, Aleppo, intensified.
Government warplanes and ground forces pounded it with bombs and mortar rounds as rebel fighters fought off soldiers in the narrow alleys of the city's old quarter.
The British-based Syrian Observatory for Human Rights activist group said the clashes in Aleppo were concentrated in several tense neighborhoods — Masaken Hanano, Bustan al-Qasr, Sukkari, and Maysar. It reported injuries and damage to buildings, but gave no specific figures.
Another activist group, the Local Coordination Committees, said the government was making heavy use of warplanes in attacking rebel areas.
Last week, rebel commanders claimed to have destroyed several helicopters during attacks on two military airports in Idlib province.
Videos that activist groups said showed the aftermath of the attack raised the possibility that rebel fighters had captured shoulder-fired anti-aircraft missiles, although it was not clear whether some of the missiles had the necessary components to make them functional.
Rebel groups have been eager to acquire the weapons to counter the government's increasing use of warplanes and helicopters in the conflict.
In recent weeks, there have been several sightings of the shoulder-fired anti-aircraft missiles, possibly smuggled across Syria's borders or acquired after raids on government arsenals.
The sightings have raised concerns about the spread of the weapons, which can be used against commercial jets.
For the moment, there has been little evidence the weapons have changed the course of the conflict.
Since the start of August, rebel fighters have claimed that they have shot down at least three government aircraft, including two warplanes and a helicopter, with fighters in at least two cases saying the aircraft were brought down with heavy machine-gun fire. The government has blamed mechanical failure for the crashes.
Also Saturday, Syria's official state news agency said the government had released more than 300 people it had detained recently during fighting in the Damascus suburbs of Homs, Aleppo, and Daraa.
The news agency said the detainees were "involved in recent events" but had committed no crimes. It was not clear why they had been held.