NEW YORK • The United Nations Security Council has unanimously adopted a resolution endorsing a political transition to end Syria's bloody civil war, while sidestepping a list of divisive issues topped by the fate of President Bashar al-Assad.

Foreign ministers from 17 countries, who gathered in New York on Friday before the council's session, also failed to bridge differences, including which opposition factions should be branded "terrorists".

That designation would exclude a group from the political process while implicitly endorsing it as a target for the separate campaigns of air strikes by Russia and a US-led coalition. Instead, the world powers settled for a resolution calling on warring sides to start peace talks "in early January".

Still, the resolution - the first adopted by the 15-member Security Council that focused on a political track for Syria - may give momentum to the talks.

Russia previously vetoed four attempts by Western powers to censure the Syrian regime while agreeing on measures to destroy chemical weapons and convene peace talks in Geneva.

"It is very good that the US and Russia are trying to work together even if they have very different outcomes in mind," Dr Joshua Landis, director of the Centre for Middle East Studies at the University of Oklahoma, said in an e-mail.

"Up until now, both sides have believed that an escalation in fighting could help turn the balance of power in their favour and bring their opponents to their knees," he added.

The Security Council "is sending a clear message to all concerned that the time is now to stop the killing in Syria and lay the groundwork for a government that the long-suffering people of that battered land can support", US Secretary of State John Kerry said at the Security Council session.

Mr Kerry told reporters later that US-Russian cooperation in preparing for the peace talks may open the way for greater military coordination between the two countries over Syria.

But he added that Russia must focus its air strikes on Islamic State in Iraq and Syria (ISIS) terrorists rather than some anti-Assad groups that the US and its allies back as moderates.

Russia's Foreign Minister Sergei Lavrov told the Security Council that "only the Syrians can decide their own fate" and "we all agree that terrorists have no place at the negotiating table".

He said the resolution "should open the way to a broad anti-terrorist front", including the Syrian government and Kurdish militias.

Chinese Foreign Minister Wang Yi, who is in Berlin, described the UN resolution as "very balanced".

The resolution urges member states to support ceasefire efforts and end attacks on civilians, and for all parties to allow access for humanitarian aid.

It also calls for a transitional government within six months and elections within 18 months.

Left unclear was whether the early January deadline for the start of talks between the opposition and government can be met.

One big obstacle to putting a deal in place may be determining which of the disparate rebel groups would participate in the talks, and whether they would agree to come to the table at all without a guarantee of Mr Assad's exit.

Nor has Mr Assad said he would participate - though he will be under pressure from Russia and Iran to do so.

BLOOMBERG, NEW YORK TIMES