The large number of deeply divided rebel groups is one of the main obstacles to a UN mission's efforts to broker an end to Syria's 18-month crisis, the Damascus representative of the new international envoy says.

Canadian diplomat Mokhtar Lamani, who represents special envoy Lakhdar Brahimi in the Syrian capital, told The Associated Press in an interview that a solution to the country's crisis remains very difficult because of the "high level of mistrust between all parties." Most opposition groups say they will accept nothing less than President Bashar Assad's departure from power, while the regime says its opponents are working as part of a foreign conspiracy.

Canadian diplomat Mokhtar Lamani, seen here in 2007, heads the Damascus office of the UN envoy to Syria. Divisions among the Syrian opposition hinder efforts at progress, he says. (Amr Nabil/Associated Press)

With every diplomatic effort so far failing to halt the violence, Syria's civil war has descended into a deadly daily grind as the regime and the rebels trying to overthrow Assad both try to gain the upper hand.

Some of the heaviest fighting Monday took place in the northern city of Aleppo, where rebels recently launched a new offensive to capture the country's commercial capital. A tourism official based in Aleppo said more than 500 historic shops have been burnt since Saturday in the city's centuries-old covered market, adding that the giant doors of the nearby citadel were damaged although the structure is intact.

Aleppo-based activist Mohammed Saeed said 12 people were killed when troops shelled a mosque in the city early Monday. A video posted online showed wounded worshippers being rushed away. Another video showed the Osman bin Madoun Mosque later in the day with its green carpets stained with blood.

Death toll on Monday put at 95

The Observatory said 40 people were either killed or wounded in Aleppo on Monday, while the LCC put the death toll nationwide at as many as 95 by Monday afternoon.

Northwest of Aleppo, government warplanes bombed the town of Salqin, killing at least 21 people including five children, activists said. The Local Co-ordination Committees, another activist group, put the death toll at 30.

Salqin is located some six kilometres from the border with Turkey in Idlib province, which has seen intense clashes between government troops and rebels in recent months.

Footage posted online by activists showed several mutilated bodies in the back of a pickup truck as a man shouts that his son was killed. A second video showed three dead children on the floor of what appeared to be a hospital.

The government severely restricts access to the country, and the authenticity of the videos could not be independently verified.

New envoy replaces Kofi Annan

Brahimi, a veteran Algerian diplomat who previously served as a UN envoy to Afghanistan and Iraq, waded into Syria's complicated diplomatic landscape last month when he replaced Kofi Annan, the former UN chief whose peace plan for Syria failed to end the violence that activists say has so far killed more than 30,000 people.

Lamani said Brahimi, who visited Damascus last month, will pay a second visit to Syria soon and will tour the country. Asked whether he still sees hope of a political solution in Syria despite the bloodshed, Lamani said: "I think maybe the time will be too long, but I hope [so] … and this is what I am here for because I hope that in the end there would be some light."

The uprising against Assad that erupted in March last year began with anti-government protests but has gradually morphed into a civil war that has spread across the country. Since then, rebels have taken over patches of territory, mostly near the northern border with Turkey.

Lamani noted that he had recently visited the central province of Homs and the southern province of Daraa, where he with met representatives of armed groups in the town of Rastan, a rebel stronghold in Homs that was among the first areas to take up arms against Assad's regime. He did not provide any details of his meetings.

He said that some of the main obstacles to brokering a resolution to the conflict are divisions among rebels and opposition groups. There is a vast array of such groups inside and outside the country, and relations among them have been dogged by infighting and mutual accusations of treachery. The rebels include army defectors and gunmen who work under the ragtag Free Syrian Army.

Despite months spent trying to cobble together a common front, attempts to unite the opposition have so far failed.

"There are so many opposition parties inside and outside Syria in addition to the armed groups," Lamani said in Damascus. "This is a little bit very dangerous and complicating our mission because of this kind of fragmentation."

Historic Aleppo markets devastated

Rami Martini, chief of Aleppo's Chamber of Tourism, said three historic markets which he identified as Niswan, Darb and Istanbul "were totally burnt and they consist of more than 500 shops."

Martini, the tourism official, blamed anti-government gunmen for the fires in the market, saying opposition forces "hate history." He said the government as well as Arab and international funders spent $300 million to renovate the Aleppo market between 1993 and 2010.

The Aleppo bazaar, a major tourist attraction with its narrow stone alleys and stores selling perfume, fabrics and spices, had been the site of occasional gun battles and shelling for weeks. But amateur video posted Saturday showed wall-to-wall flames engulfing wooden doors as burning debris fell away from the storefronts. Activists said hundreds of shops were affected, in the worst blow yet to the city's historic centre.

Aleppo's walled old city with a medieval covered market, or souk, was recognized by the UN cultural agency as a World Heritage site, one of six in Syria.

"The historical losses in the market are invaluable and the hope is that the market be renovated in the future," Martini told The Associated Press by telephone from Aleppo.

Syria's foreign minister at UN

Meanwhile on Monday, Syrian Foreign Minister Walid al-Moallem accused some UN. Security Council members of supporting "terrorism" in the country in an attack clearly aimed at the U.S. and its allies who are supporting the opposition.

Addressing the UN General Assembly's annual ministerial meeting, al-Moallem said peace requires action by Turkey, Saudi Arabia, Qatar, Libya and others to stop arming, financing and supporting the opposition — as well as by Syria.

The Security Council's major powers are deeply divided over the 18-month Syria conflict. Russia and China, key backers of the Assad regime, have vetoed three resolutions by the U.S., Britain and France, which back the opposition and have called for Assad to be replaced.

Al-Moallem said countries are interfering in Syrian domestic affairs.

"We heard calls from this podium, and on other platforms, some calls from those who are ignorant of the facts or maybe ignoring them, or also from those who are shareholders in exacerbating them, that invites the president of the Syrian Arab Republic to step down," he said. "This is a blatant interference in the domestic affairs of Syria, and the unity of its people and its sovereignty."

He also asked aloud to what extent statements by Qatar, Saudi Arabia, Turkey, the United States and France "that clearly induce and support terrorism in Syria with money, weapons and foreign fighters, are in line with the international responsibilities of these countries in combating terrorism."

Al-Moallem called for a political solution and Syrian-led dialogue to agree on a road map to "a more pluralistic and democratic Syria."

He invited the opposition to "work together to stop the shedding of Syrian blood."