The United States on Sunday voiced confidence that Syria's opposition National Coalition group would attend upcoming peace talks in Switzerland with representatives of Bashar al-Assad's regime.
"I am confident personally that the Syrian opposition will come to Geneva," US Secretary of State John Kerry said after a Paris meeting of the 11-nation "Friends of Syria" group attended by Coalition leader Ahmad Jarba.
"It was a very constructive meeting today (with Jarba). I am confident that he and others will be in Geneva. I am counting on both parties to come together."
The upbeat tone contrasted with the more cautious note struck by other ministers involved in Sunday's talks, which marked the start of a new round of diplomacy aimed at ending the conflict.
Kerry is due to meet Monday with his Russian counterpart Sergei Lavrov and the UN-Arab League envoy on Syria, Lakhdar Brahimi, as well as holding further talks with Jarba.
Kerry's comments came after Jarba's coalition was offered assurances that there will be no place for Assad in a transitional government they hope to see emerge from the so-called Geneva II talks due to start in Montreux on January 22.
In a statement, the Friends of Syria group said that once a transitional government is established .... "Assad and his close associates with blood on their hands will have no role in Syria."
The Swiss talks have been organised in an attempt to revive the idea of moving to a transitional government including figures from the current regime and the opposition.
Whether that could involve Assad himself is an issue that has generally been fudged in the past and may have the potential to capsize the negotiations: Assad's aides have repeatedly said they have no intention of coming to Switzerland to hand over power.
Kerry would not be drawn on what would happen if Assad pulled out of the talks.
"With respect to the Assad regime we have been told from day one they allegedly are prepared to negociate," he said.
"I am not getting into consequences other than to say that this the test of credibility of everybody."
Jarba indicated that he had been reassured by the tone of Sunday's discussions.
"We all agreed that there is no future for Bashar al-Assad and his family in Syria," he said.
"His departure is inevitable."
Jarba added: "We are at a crossroads today in the framework of international decisions regarding the Syrian revolution.
"We have passed a milestone on the way to the end of the regime."
At least 700 killed in fighting with al-Qaeda linked group
Jarba has previously called for Assad to stop using heavy weapons, lift sieges on a number of opposition-held areas and allow the opening of humanitarian corridors as a show of good faith ahead of any talks.
There has been no sign of progress on those issues but, with little prospect of securing a military victory after nearly three years of fighting, the opposition has little alternative but to enter negotiations.
French Foreign Minister Laurent Fabius added: "It is important that the Geneva II meeting takes place and succeeds. The only solution to the Syrian tragedy is a political solution."
British Foreign Secretary William Hague said it was in the opposition's interests to attend the talks and try to end a conflict that has caused 130,000 deaths and created more than two million refugees.
"In the end, there's got to be a political solution in Syria," Hague told Sky News from Paris. "This is going to put the Assad regime on the spot if everybody turns up at those peace talks."
The balance of power in the conflict in Syria appears to have tipped in Assad's favour over the last week as deadly clashes have erupted between the mainstream opposition and an Al Qaeda-linked group, the Islamic State of Iraq and the Levant (ISIL), with which they were previously allied.
According to NGOs monitoring the conflict, at least 700 people have been killed since the fighting started January 3 and the ISIL is threatening to abandon frontline positions in the area around Syria's second city, Aleppo.
Hopes of progress towards peace in Syria rose last year when Assad agreed to give up the regime's chemical weapons after the West pulled back from the brink of threatened military intervention.
That deal resulted in Syria's ally Russia becoming a pivotal player in the efforts to end the conflict.
Monday's Kerry-Lavrov meeting is expected to focus on whether Iran, which has been instrumental in propping up Assad, should have any role in peace talks further down the line.