US Secretary of State John Kerry arrived in Paris Monday for private talks with Russian Foreign Minister Sergei Lavrov as the two men seek to bring together the warring sides in Syria to end the bloodshed.
Kerry was to brief his Russian counterpart on a Friends of Syria meeting in Amman last week, at which the 11 ministers of the core group told Syrian President Bashar al-Assad that refusing to negotiate was not an option.
In a statement in the early hours of Thursday after marathon diplomatic talks, the Friends of Syria warned Assad that if he refused to back moves to end the fighting they would boost their support for the opposition.
The group "emphasised that until such time as the Geneva meeting produces a transitional government, they will further increase their support for the opposition and take all other steps as necessary," the statement said.
It also voiced "deep concern over the deteriorating humanitarian conditions in Syria, as well as the threat... to the stability and security of neighbouring countries hosting Syrian refugees."
More than 94,000 people have been killed in the war now in its third year, which is threatening to spill over Syria's borders with the growing engagement of Hezbollah militants fighting on the regime side.
Kerry and Lavrov last met earlier this month in Moscow, at which they agreed to work in tandem to bring together the Assad regime and the opposition in a peace conference with the aim of working towards a political transition.
Kerry also wants to hear from Lavrov about his discussions with the Assad regime, which according to the Russians has in principle agreed to attend the conference.
Syrian opposition leaders meanwhile are meeting in Istanbul to choose a new leadership and parliamentary composition, and have so far not decided whether to attend peace talks, which will most likely be held in Geneva next month under the aegis of the United Nations.
The US top diplomat has warned that unless the two sides can be persuaded to come to the table the world would witness "the continued tragic disintegration of a country that will go down further into more violence and more bloodshed and more destruction."
After their talks, French Foreign Minister Laurent Fabius was to host a private dinner with the two men.
Kerry arrived from Amman and is on the last leg of an eight-day overseas trip, which has taken him so far to Oman, Jordan, Israel, the West Bank, and Ethiopia.
He is due to fly back to Washington on Tuesday.