The European Union will impose harsher sanctions on Syria, a senior EU official has said, as Russia tried to broker talks between the vice president and the opposition to calm violence.

Activists reported at least 50 killed in the regime's siege of the restive city of Homs.

Russia, a close ally of Syria, and the West are pushing down starkly different paths in trying to deal with Syria's nearly 11 months of bloodshed.

After blocking a Western and Arab attempt to bring UN pressure on President Bashar Assad to step down, Russia has launched a bid to show it can resolve the turmoil.

Moscow is calling for a combination of reforms by the regime and negotiations, without calling for Assad to go. Its provisions are so far finding no traction with the opposition, which dismisses promises of reform as empty gestures, refuses any negotiations while violence continues and says Assad's removal is the only option in the crisis.

Russian Prime Minister Vladimir Putin said outside forces should let Syrians settle their conflict "independently".

"We should not act like a bull in a china shop," Mr Putin said, according to the ITAR-TASS news agency.

"We have to give people a chance to make decisions about their destiny independently, to help, to give advice, to put limits somewhere so that the opposing sides would not have a chance to use arms, but not to interfere."

Russian Foreign Minister Sergey Lavrov, who met with Assad in Damascus, told reporters in Moscow that the Syrian president delegated to his vice president, Farouk al-Sharaa, responsibility for holding a dialogue with the opposition.

Mr Lavrov blamed both Assad's regime and opposition forces for instigating the violence, which the UN says has killed well over 5,400 people. "On both sides, there are people that aim at an armed confrontation, not a dialogue," Mr Lavrov said.