International peace envoy Kofi Annan was expected to head to China on Monday after asking Russia to back his mission to end fighting in Syria despite Moscow's differences with Western and Arab states over who is to blame for the conflict.
Russia said Annan had its full support and that his mission could be the last chance to avoid a protracted and bloody civil war but would need more time.
It also suggested foreign support for Syrian President Bashar al-Assad's foes was the main obstacle to peace, while Western and Arab officials prepared for a "Friends of Syria" meeting on ways to help the disparate opposition.
Forces loyal to Assad pounded Homs and clashed with rebels in other opposition strongholds on Sunday, fighting which Syrian activists said killed 27 people, 15 of them civilians. Syrian state media said six "terrorists" had died.
Annan's spokesman, Ahmad Fawzi, said he had "very candid and comprehensive discussions" in Moscow. Annan was "grateful for Russia's firm support for his mediation efforts in order to reach a swift and peaceful solution to this bloody conflict" and asked Russia to continue providing support.
It was not clear whether Moscow would increase pressure on Assad to comply with Annan's peace plan, which includes demands for a ceasefire, the immediate withdrawal of heavy armour from residential areas and access for humanitarian aid.
Russia and China have shielded Assad from U.N. Security Council condemnation by vetoing two Western-backed resolutions over the bloodshed, but approved a Security Council statement this week endorsing Annan's mission.
The former UN chief was expected to leave Moscow for China, which joined Russia in the vetoes, on Monday.
Western and Arab leaders are due to meet in Istanbul on April 1 to discuss a political transition and the Arab League and Turkey were pressing various parts of the Syrian opposition to gather in the city on Monday and Tuesday to try to unite.
Waleed al-Faris, an opposition activist from Homs, told Reuters Sunday's shelling, using tank and mortar fire, was the worst he had seen. "There are ten dead and hundreds wounded," he said.
Government forces and rebels also clashed in the southern province of Deraa, birthplace of the revolt.
"Thousands of soldiers and over a hundred military vehicles are attempting to enter the area of Lahat in Deraa province today, but they are clashing with rebels," said Rami Abdelrahman, head of the Syrian Observatory for Human Rights.
A US-based human rights group accused Assad's forces of using human shields in northern Syria in their efforts to crush the rebellion, which began more than a year ago.
Human Rights Watch said people were forced to walk in front of advancing troops and that residents reported government forces placing children on tanks and inside security buses.
"The Syrian army's use of human shields is yet another reason why the UN Security Council should refer Syria to the International Criminal Court," said Ole Solvang, a HRW emergencies researcher.
It was impossible to verify reports independently because Syrian authorities have prevented foreign journalists and human rights workers from entering affected areas.
The United Nations says around 8,000 people have been killed. Syria says rebels have killed about 3,000 members of the security forces and blames the violence on "terrorist" gangs.
Russian President Dmitry Medvedev, who will join US President Barack Obama for a nuclear security summit in South Korea on Monday, told Annan, the Syria envoy for the United Nations and Arab League, he appreciated his efforts.
"This may be the last chance for Syria to avoid a long-lasting and bloody civil war. Therefore we will offer you our full support at any level and in various ways in those areas, of course, in which Russia is capable of providing support."
Obama, already in Seoul, discused how to get non-lethal aid to the Syrian opposition on Sunday with Turkish Prime Minister Tayyip Erdogan.
Western and Arab states have urged Assad to step aside to end the violence. Russia, a close ally of Assad, said he is ready to talk to his foes about reform and it is the rebels who must be pressed to negotiate.
Russian Deputy Foreign Minister Gennady Gatilov said Annan's mission must be given more time before the Security Council considers further action. The Security Council statement this week threatened Syria with unspecified "further steps" if it failed to comply with Annan's plan.
"There are no deadlines, we need to see how the situation develops," the Interfax news agency quoted Gatilov as saying.