International envoy Kofi Annan was meeting Chinese leaders in Beijing on Tuesday to discuss how to end the bloodshed in Syria, while opposition factions at talks in Turkey mulled a united front against the Damascus regime.

Syrian rebels man a check-point in northern Syria's Idlib region, on March 18, 2012. The UN is investigating reports that Syrian rebels have been using child soldiers in their battle against President Bashar al-Assad's forces. (AFP Photo/Frederic Lafargue)

The Syrian Observatory for Human Rights said one woman was killed by a stray bullet near Damascus while the other two died in Maaret al-Numan in the northwest Idlib province, where four soldiers were killed in clashes with rebels.

Another civilian was killed by sniper fire in the flashpoint central city of Homs.

A UN official, meanwhile, said the organisation was investigating reports that Syrian rebels were using child soldiers in their battle against President Bashar al-Assad's forces.

UN-Arab League envoy Annan was to hold talks with Chinese Premier Wen Jiabao on a plan calling for a UN-supervised halt to fighting in Syria and a transition to a more representative political system.

At the weekend he met officials in Russia, which along with Beijing has provoked international fury for twice blocking UN Security Council resolutions condemning the Assad regime.

Beijing is also pushing for its own six-point plan, calling for an immediate end to the conflict and for dialogue between the regime and opposition.

In Istanbul, Syrian opposition factions including the main Syrian National Council (SNC) were meeting for a second day to agree on common objectives for their nation's future ahead of a weekend "Friends of Syria" conference.

Syria's fragmented opposition has struggled to remain united in the face the regime's deadly crackdown and the Istanbul talks are aimed at shoring up ranks and secure international recognition.

For council member Omar Idlibi the main goal is "to drop the legitimacy from the Syrian regime," followed by recognition of the SNC and the rebel Free Syrian Army (FSA).

Annan has stressed there could be no deadline to ending the year-long crisis, which monitors say has left more than 9,100 people dead since it erupted in March 2011, even as the opposition seeks the ouster of Assad.

"I think only Syrians should decide the issue of Assad's resignation," Annan told Russian news agencies after Sunday's talks with Russian President Dmitry Medvedev.

"It's important to sit all Syrians behind a negotiating table," he said, according to a Russian translation of his remarks, adding it was "incorrect to give any deadlines" for ending the violence in Syria.

Medvedev had warned on Sunday that Annan represented the last chance for avoiding a civil war in Syria, promising him Russia's full support.

Annan's peace plan calls for a halt to fighting, with the government pulling troops and heavy weapons out of protest cities; a daily two-hour humanitarian pause to hostilities; and access to all areas affected by the fighting.

It also calls for the release of people detained in the uprising. However it imposes no deadline on Assad, nor does it call for his resignation.

The former UN chief's spokesman said in a statement Monday that Damascus had responded to the six-point proposal to end the crisis. "Mr Annan is studying it and will respond very shortly," he said.

Medvedev, whose government has come under increasing pressure to act on Syria, discussed the crisis in Seoul with US President Barack Obama on Monday.

Afterwards, Obama acknowledged there had been disagreements in recent months between the United States and Russia, an ally of Assad's regime.

But he said both agreed "we should be supportive of Kofi Annan's efforts to end some of the bloodshed that is taking place in Syria", and that the goal was to have a "legitimate" government in Damascus.

US Secretary of State Hillary Clinton is to visit Saudi Arabia on Saturday and Sunday for talks on Syria, State Department spokeswoman Victoria Nuland said.

The bloodshed in Syria has been unrelenting with clashes nationwide Monday claiming the lives of at least 32 people, including 19 civilians, according to the Britain-based Observatory.

In recent weeks the violence has creeped closer to the capital, with activists and monitors now giving almost daily reports of clashes in and around Damascus which so far had been largely spared.

On Monday at least seven soldiers and five civilians were killed in the Damascus province towns of Harasta and Zabadani.

Reports of abuse by the military opposition also surfaced, with a UN official saying the FSA was using child soldiers, although the claims could not be immediately verified.

"We are receiving allegations of children with the Free Syrian Army," said UN special representative for children in armed conflict, Radhika Coomaraswamy."