Syrian air and ground forces hit Aleppo

Fighting is raging in Syria as veteran UN diplomat Lakhdar Brahimi calls on the government to realise the need for change is "urgent".

Syrian warplanes and ground forces have pounded the country's largest city, Aleppo and a new UN envoy has called for urgent change.

In an interview with al-Arabiya television on Saturday, New York-based Lakhdar Brahimi told the Syrian government it must respond to the "legitimate" demands of the Syrian people.

He said President Bashar Assad's regime should realise the need for change was both "urgent" and "necessary."

Brahimi's comments came on his first day as the new UN envoy to Syria, replacing Kofi Annan who quit after his six-point plan including an April 12 ceasefire failed to stop the bloodshed.

Brahimi, a former Algerian foreign minister who has been a UN envoy to Afghanistan and Iraq, said his first task would be to overcome the divisions in the Security Council and get it to speak "with a unified voice".

The Britain-based Syrian Observatory for Human Rights said the clashes in Aleppo were concentrated in several neighbourhoods - Hanano, Bustan al-Qasr, Sukkari and Maysar. It reported injuries and damage to buildings.

Another activist group, the Local Co-ordination Committees, said the government was using planes to attack 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.

A rebel push in Aleppo dubbed "Northern Volcano" was 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.

In the east, the observatory reported rebels captured an air defence 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.

Despite the government's control of Damascus, opposition fighters continue to stage attacks using hit-and-run tactics in neighbourhoods where they enjoy popular support, activists say.

Early on Saturday, government forces bombarded the capital's southern neighbourhood of Tadamon after street fighting with rebels there, the observatory said. Troops also shelled the nearby neighbourhood of Hajar Aswad.

The state-run news agency SANA said an army general had been killed by "terrorists" who placed a bomb under his car parked in front of his Damascus home and detonated it when he got into the vehicle.

The observatory said the bodies of five unknown people were found in the neighbourhood of Qadam, shot execution-style.

Other clashes were reported in Idlib province on the border with Turkey, in Daraa near the Jordanian frontier, and in the central province of Homs near Lebanon, activists said.

SANA reported on Saturday that 225 detainees who took part in anti-government protests had been released. The amnesty by authorities is the second in a week as some 378 prisoners from Damascus and the central province of Homs were freed on Monday.

Activists say tens of thousands of Syrians have been detained over the past 18 months.