China and Russia on Thursday urged all parties in Syria to "stop violence" after suicide attackers detonated massive bombs in Damascus during morning rush hour, killing at least 55 people.

Syrian President Bashar al-Assad's government blamed the attacks -- which also wounded nearly 400 people -- on "terrorists", while the opposition accused his regime of staging the bombings to threaten UN observers.

"We ask all parties to stop violence and cooperate with (UN-Arab League special envoy Kofi) Annan and UN special envoys," Russian Foreign Minister Sergei Lavrov told reporters after Beijing talks with counterpart Yang Jiechi.

China's foreign ministry spokesman Hong Lei also called for an end to the violence and condemned a Wednesday bomb attack on UN observers in the conflict-torn state that wounded 10 soldiers escorting them.

Lavrov also told reporters that Russia would not change its stance on the Syrian situation.

Beijing and Moscow -- both long-standing allies of Damascus -- drew international criticism earlier this year for vetoing two UN Security Council resolutions against Assad's regime.

They have since backed Annan's efforts to bring peace to Syria in the form of a six-point proposal agreed by Damascus that includes a ceasefire and withdrawal of troops.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, says almost 12,000 people, mostly civilians, have been killed in Syria since an anti-regime revolt broke out in March last year.

About 800 of them have died since the truce brokered by Annan was supposed to have taken effect on April 12.

Lavrov -- according to a Chinese translation of his comments -- appeared to imply that some countries were encouraging rebels in Syria to fight on.

"Some countries have asked rebels not to compromise and continue to cause trouble," he said, adding these unnamed nations hoped this would cause "external forces" to intervene.

"This cannot be accepted and the UN Security Council will not allow it to happen."

Both Yang and Lavrov said they had discussed an upcoming visit to China by Vladimir Putin, who returned to the Russian presidency on Monday after four years as premier. They made no mention of the timing.