The "Friends of Syria" group of Western and Arab foreign ministers meets in London on Tuesday hoping to persuade opposition leaders to attend a planned peace conference in Geneva next month.
British Foreign Secretary William Hague said the London meeting was aimed at persuading Syria's fractious opposition to have a "united position" for the conference in the Swiss city, pencilled in for 23 November.
The Syrian National Council, a key member of the Syrian National Coalition, has already said it opposes the conference and threatened to quit the opposition grouping if the regime of President Bashar al-Assad takes part in the UN-backed Geneva II conference.
Tuesday's talks group the so-called London 11, the core group of the Friends of Syria that consists of Britain, Egypt, France, Germany, Italy, Jordan, Qatar, Saudi Arabia, Turkey, the United Arab Emirates and the United States, together with opposition leaders.
"The National Coalition has said they will go to Geneva. Within the National Coalition, there is the National Council which has said it's opposed to doing that. It will be resolved among the opposition through a general assembly of representatives in a couple of weeks time," Hague told BBC radio.
"So we are meeting ahead of that to encourage them to have a united position, to show that those in the world among Westerners and Arab nations who understand and sympathise with their position in Syria have a united position, that they should go to the Geneva peace talks and stop the blood and talk together as Syrians," Hague added.
But Assad dealt an early blow to peace hopes, saying in an interview Monday that he was willing to run for re-election in 2014 and that the factors are not in place for the Geneva II conference to succeed.
US Secretary of State John Kerry earlier said that the Syrian opposition would never agree to Assad staying in power.
"He has bombed and gassed people in his country.... How can that man claim to rule under any legitimacy in the future?", Kerry said after talks with Arab League officials in Paris.