A Jordanian militant leader linked to al-Qaeda warned Sunday that his extremist group will launch "deadly attacks" in neighbouring Syria to topple President Bashar Assad, as Damascus lashed out at France for backing Syrian rebels.

In a speech delivered to a crowd protesting outside the prime minister's office in Amman, Mohammad al-Shalabi, better known as Abu Sayyaf, told Assad that "our fighters are coming to get you."

Abu Sayyaf is the head of the Salafi Jihadi group, which produced several al-Qaeda linked militants who fought U.S. forces in Iraq and Afghanistan over the past 10 years. They are also blamed for the 2002 assassination of US aid worker Laurence Foley outside his Amman home.

The militant leader was himself convicted in 2004 of plotting attacks on Jordanian air bases hosting American trainers, but served his term and was released last year.

Militants linked to al-Qaeda, many from Iraq but also reportedly several from Jordan, are believed to have made inroads among Syrian rebels as the civil war there intensifies.

The warning came hours after Syrian Foreign Ministry spokesman Jihad Makdessi criticized France, saying its growing support for the opposition does nothing but undermine the mission of the new UN envoy tasked with brokering a diplomatic solution to the conflict.

France, Syria's one-time colonial ruler, has been one of the most outspoken Western critics of the Assad regime, and announced earlier this month that it has begun sending direct aid and money to five rebel-held Syrian cities as part of its intensified efforts to weaken Assad. It was the first such move by a Western power amid mounting calls for the international community to do more to prevent bloodshed.

Makdessi said France suffers from "schizophrenia" in its approach to the country's conflict — supporting both the UN-backed peace process and the "militarization of the crisis."

French officials have acknowledged providing communications and other non-lethal equipment to Syrian rebel forces, but say they won't provide weapons without international agreement. France played a leading role in the international campaign against Libya's dictator Moammar Gadhafi last year.

Diplomacy fails

Diplomatic efforts to solve the seemingly intractable conflict have failed so far. A peace plan by former UN Secretary-General Kofi Annan never got off the ground and Annan quit his post as special UN envoy. He was replaced on Sept. 1 by Lakhdar Brahimi, a 78-year-old former Algerian foreign minister.

Makdessi said Sunday that Syria is "fully committed to co-operating with Brahimi."

The Assad regime made similar public statements of co-operation when it signed on to Annan's peace plan, only to frequently ignore or outright violate its commitments by refusing to pull its troops out of cities and cease its shelling of opposition areas.

Makdessi said the only way to end the Syrian conflict is a "cease-fire by all parties."

U.S. Secretary of State Hillary Rodham Clinton says Washington will continue to put pressure on Russia to side against its ally Syria. (Jim Watson/Associated Press)

At the end of the APEC summit in Russia, U.S. Secretary of State Hillary Clinton said she would continue to try to convince Moscow to back increased international pressure on Syrian President Bashar Assad — even if such a step is unlikely.

Russia on Saturday rejected her call for UN sanctions against the Assad regime. Clinton said if the Russians refused to go along the United States and its friends would boost their support for the Syrian opposition.

"The United States disagrees with the approach on Syria," she told reporters at a news conference. "We have to bring more pressure to bear on the Assad regime to end the bloodshed and begin a political, democratic transition."

The Obama administration has been hoping to jack up pressure on Assad at the upcoming United Nations General Assembly session and potentially introduce a new UN Security Council resolution that would include sanctions. Russia and China have blocked three previous similar resolutions because they could lead to sanctions.

Support among Sunnis

In Jordan, security officials say in private that Abu Sayyaf's group comprises several hundred activists. The group regularly faces crackdowns and arrests, but longterm detention without the filing of criminal charges — a tactic that has been used by other Arab states to keep radical Islamists in prison indefinitely — is not regularly used against the Islamists.

Syria's rebels enjoy widespread sympathy across Sunni Arab countries. Western officials say there is little doubt that Islamist extremists, including fighters from other Muslim countries, have made inroads in Syria as instability has spread. Al-Qaeda-style suicide bombings have become increasingly common.

Many of the foreign jihadists going to Syria are believed to come from Iraq, but in June Jordanian police said they arrested two members of Abu Sayyaf's group near the northern border as they tried to cross into Syria.

Meanwhile, the Syrian Observatory for Human Rights — a Britain-based monitoring group — said fighting raged across Syria on Sunday, with at least 28 reported killed and scores wounded.

FSA soldier fires on Syrian Army positions in Aleppo, Syria, Saturday, Sept 8, 2012. (Manu Brabo/Associated Press)

It said an air raid on a residential district in the commercial capital of Aleppo in the north killed at least four people, wounded several more and flattened a residential building. The Free Syrian Army said the strikes came hours after rebels overran army barracks in the Hananu neighbourhood.

Activists also reported clashes between government forces and rebels in a Palestinian refugee camp on the outskirts of the capital, Damascus, in the central city of Homs, in the northern city of Idlib and in the eastern city of Deir el-Zour.

The Observatory said the heaviest fighting was taking place in Homs, where two bombs exploded in a bus, killing and wounding several military officers and civilians. It did not elaborate.

The Syrian state news agency put the death toll in the explosion at four, including a woman. It said a roadside bomb struck the bus as it was travelling toward Damascus along the Mussyaf-Homs highway. It said the explosion wounded 35 people and left a large crater in the ground.