The divided Syrian opposition is meeting Friday in Istanbul to decide on its participation in next week's peace talks, which President Bashar al-Assad's government has said it will attend, dpa reported.
In Moscow, Russian Foreign Minister Sergei Lavrov was meeting with his Syrian counterpart, Walid al-Muallem, in a flurry of last-minute diplomacy ahead of the international conference.
The National Coalition has repeatedly said the conference in Switzerland should lead to a transitional government with no future role for al-Assad and his family.
The government has rejected this demand.
US Secretary of State John Kerry urged the coalition to participate, saying Thursday that the talks were "the only way to bring about an end to the civil war that has triggered one of the planet's most severe humanitarian disasters and which has created the seeding grounds for extremism."
The Syrian National Council, a key member of the umbrella group, has rejected the conference and threatened to withdraw from the coalition if it decided to join the talks.
The international meeting in Montreux will seek to negotiate an end to the Syrian conflict, now in its third year.
The United States and Russia have been working on organizing the conference since the middle of 2012. The goal is to establish a process to form a transitional government, which must be agreed to by all sides, Kerry said.
The Syrian uprising started in March 2011 with anti-government protests, but descended into civil war after al-Assad's regime sought to quell the demonstrations with violence.
The Britain-based Syrian Observatory for Human Rights estimates that at least 130,000 people have been killed since. In July, the UN put the death toll at 100,000 and has now stopped counting the dead.