The U.N.'s new envoy to Syria told President Bashar Assad's regime on Saturday that change is both "urgent" and "necessary" and that it must meet the "legitimate" demands of the Syrian people, words that will not win the seasoned Algerian diplomat and international trouble shooter 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 on military operations to create a better atmosphere for his peace mission.

His comments, made in New York, came as activists said rebels captured an air defense facility in the east of the country near the border with Iraq. The battle for control of Syria's largest city Aleppo meanwhile intensified, with government warplanes and ground forces pounding it with bombs and mortar rounds as rebel fighters fought off troops in the narrow alleys of the city's old quarter.

"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," Brahimi told al-Arabiya television in an interview.

"The need for change is urgent and necessary. The Syrian people must be satisfied and their legitimate demands are met," he said.

The latest violence in Aleppo shows that government forces are still struggling to regain full control of the city from the lightly-armed rebels nearly five weeks after they stormed their way into the city in a surprise offensive.

The Syrian Observatory for Human Right activist group said Saturday's 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.

For over a year after the uprising against Assad's rule began nearly 18 months ago, 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 to a stalemate in Aleppo, the nation's commercial capital and home to 3 million people.

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. The opposition has claimed advances in the area in recent days. A video released by activists showed soldiers purportedly captured by rebels at the post.

The authenticity of the video could not be independently confirmed.

There was no immediate response from the Syrian government to the comments made by 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.

Brahimi said he had no new ideas to end the conflict and has yet to decide when to make his first visit Damascus in his new capacity.

"I don't have anything new except insisting on the necessity of ending the violence and starting a political process that has credibility and able to bring about peace and stability for the Syrian people," he said.

"A transitional political process is what is needed. There is no disagreement inside or outside Syria that a new situation or a new political framework is needed," he said, adding that since the government and the opposition are not talking to each other, they could use him as the go-between.

Addressing himself to the opposition, he said: "Realize that the situation is both difficult and dangerous and what is important is the interest of the entire people of Syria, not individuals or groups." He was apparently alluding to the fact that most rebels fighting the government are drawn from Syria's Sunni Muslim majority. Assad and many in the nation's ruling elite are members of the Alawite sect, an offshoot of Shiite Islam. Syria's 23 million people also include a sizable Christian minority.

Brahimi refused to directly comment on statements made in Moscow Saturday by Foreign Minister Sergey Lavrov that the international community should try to persuade all sides in the Syrian conflict to stop the violence and that it would be naive or provocative to ask the Syrian government to stop the violence first.

Asked about the Russian's comments, he said: "He is responsible for his words and has the right to say that all parties must stop the violence. But, undoubtedly, I don't believe that Lavrov differs with my view that the responsibility of the government is greater than that of that the others."

The Syrian conflict has its roots in mostly peaceful street protests that started in March last year. It has since morphed into a civil war, with at least 20,000 people killed so far, according to rights activists.

In addition to Aleppo and the east, fighting continued in Damascus, where, despite the government's offensive, opposition fighters continue to stage attacks using hit-and-run tactics in neighborhoods where they enjoy popular support, activists say.

Early Saturday, government forces bombarded the capital's southern neighborhood of Tadamon following street fighting with rebels there, the Observatory said. The LCC said troops also shelled the nearby neighborhood of Hajar Aswad.

Activists also reported the discovery of dead bodies shot execution style in a Damascus suburb where fighting and shelling have been intense over the past week. They said a total of 17 bodies were found on Saturday in Kfar Batna east of the capital, a day after government forces stormed the town of some 45,000 people.

Activist Mohammed Saeed, speaking via Skype from the Damascus area, said the dead included three nurses from a local clinic that treated civilians wounded by regime shelling.

Last week, activist reports spoke of anywhere between 300 and 600 people killed in the Damascus suburb of Daraya during days of shelling and a killing spree by troops who stormed the town after heavy fighting. Saeed said another seven bodies were found in Daraya on Saturday.

In the Damascus neighborhood of Qadam, the bodies of five unidentified people were found on Saturday, all shot execution style, according to the Observatory, an activist group.

None of these reports could be independently verified.

By late Saturday, the LCC said 156 people were killed across Syria.


Associated Press correspondent Bassem Mroue contributed to this report.