The Syrian crisis topped the agenda at an EU-Russia summit on Monday as armed rebels and government forces clashed in the northwest of the country without sign of a let-up from either side.

The latest violence came a day after President Bashar al-Assad vowed to crush the 15-month uprising and the rebel Free Syrian Army (FSA) announced on Friday it was resuming "defensive operations."

In Saint Petersburg, President Vladimir Putin hosted European Union leaders for summit talks where the EU is expected to put pressure on Russia to harden its position on both the Syria and Iran crises.

Putin on Sunday evening met EU President Herman Van Rompuy and the European Commission president, Jose Manuel Barroso, in the northwestern city.

Official talks at the 29th Russia-EU summit began on Monday at Konstantinovsky Palace in the suburbs of the city, and the three leaders were due to hold a news conference at 12:40 pm (0840 GMT).

Barroso and Van Rompuy will press Putin for any hints of a softening on the Syrian crisis following his return to the Kremlin for a third term.

However, the ex-KGB agent stuck firmly to his refusal to back further action against Soviet-era ally Syria during a Friday swing through Berlin and Paris, and Moscow has signalled clearly it was still in no mood to compromise.

The foreign ministry said that the only way out of the crisis involved a cessation of violence and support for the peace plan of UN-Arab League mediator Kofi Annan.

China, which along with Russia has vetoed two UN Security Council resolutions condemning the Syrian regime, also continues to oppose outside military intervention in the country.

China's top state newspaper on Monday warned against foreign action and said the abandonment of the Annan plan could plunge the country "into the abyss of full-scale war."

However, Annan himself has demanded a "serious review" of deadlocked efforts to end the bloodshed.

Diplomats in New York said that Annan, a former UN secretary general, was stepping up pressure on the international powers to put some muscle into their support for his peace plan or find a Plan B.

The May 25 massacre of more than 100 children, women and men in Houla town, the growing threat of all-out civil war and Security Council divisions have all highlighted the failure of the international community to pressure Assad.

Moreover, as many as 2,400 of the more than 13,500 people killed since the uprising began have died since a UN-backed ceasefire, part of Annan's peace plan, began on April 12, according to the Syrian Observatory for Human Rights.

"The time is coming, if it is not already here, for a serious review," Annan told Arab League ministers in Doha on Saturday.

Annan will discuss the Syria crisis at the Security Council and UN General Assembly on Thursday. Diplomats said Annan's comments were a sign that he can see his peace initiative is failing.

Assad on Sunday dismissed allegations that his government had a hand in the Houla massacre and accused foreign-backed forces of plotting to destroy Syria.

"The masks have fallen and the international role in the Syrian events is now obvious," the president said in his first address to parliament since a May 7 legislative election.

"We are not facing a political problem but a project to destroy the country," he said, adding there would be "no dialogue" with opposition groups which "seek foreign intervention."

An official of the exiled opposition Syrian National Council condemned the address.

"Assad's speech was a declaration of the continuation of the bloody solution and the suppression of the revolution at any cost," Samir Nashar of the SNC executive office told AFP.

Clashes erupted between regime forces and rebels in Syria's Idlib province overnight, killing two opposition fighters, as explosions were reported in Damascus province, the Syrian Observatory said on Monday.

The SNC reported violence across Idlib, saying regime forces used "tanks, rocket launchers and artillery" to bombard several parts of the province.

The violence has continued unabated with 46 people killed across the country on Sunday, including 19 civilians, 19 soldiers and 8 rebels.

The bloodshed has spilled over into Lebanon, with clashes between pro- and anti-Syrian regime gunmen in the northern city of Tripoli leaving 14 people dead and 48 wounded since Saturday, according to a Lebanese security official.