BEIRUT -- Syrian warplanes and ground forces pounded the country's largest city Aleppo with bombs and mortar rounds on Saturday as soldiers clashed with rebels in its narrow streets, activists said.
The latest violence shows that government troops are still struggling to clear the city of lightly-armed rebel forces nearly five weeks after they stormed their way into it.
Activists also said rebels captured an air defense facility in the east of the country near the border with Iraq, where opposition forces have claimed advances over the past days.
The Britain-based Syrian Observatory for Human Rights said the clashes in Aleppo were concentrated in several tense neighborhoods - Hanano, Bustan al-Qasr, Sukkari and Maysar. It reported injuries and damage to buildings.
Another activist group, the Local Coordination Committees, said the government was making heavy use of warplanes in attacking rebel areas.
A video obtained by The Associated Press Television News showed rebel fighters, some in civilian clothes, in the street trading fire with government troops.
Activists say that this is the second day of a rebel push in Aleppo dubbed "Northern Volcano" targeting security facilities in the city and the surrounding province, including an artillery training school, a compound of the feared air force intelligence, and a large army checkpoint.
For over a year after the uprising against President Bashar Assad regime began in March 2011, Aleppo and Damascus stayed relatively quiet. But in July, rebels launched a brazen attack on the two cities, capturing several neighborhoods.
Government forces have regained most of the Damascus area but are being held at bay in Aleppo.
In the east, the Observatory reported that rebels captured an air defense post in the town of al-Boukamal in the oil-rich province of Deir el-Zour that borders Iraq. A video released by activists showed soldiers who said they were captured at the post after rebels took it. The authenticity of the video could not be independently confirmed.
The fighting comes as veteran U.N. diplomat Lakhdar Brahimi is due to begin a peacemaking mission, replacing Kofi Annan who quit after his six-point plan including an April 12 cease-fire failed to stop the bloodshed.
Unlike Annan, who was based in Geneva for six months, Brahimi will make his center of operations in New York, where he hopes he can better influence the U.N. Security Council to unite around a plan to end the violence.