The United States has for the first time hinted that Iran may be able to play some kind of role at proposed talks to end
the war in Syria.
US Secretary of State John Kerry said on Sunday it would be difficult to see how Iran, which did not support last year's international accord on Syria, could be a "ministerial partner" in the Geneva 2 talks, which are due to begin on January 22.
But at a news conference during a visit to Israel, he held out the possibility of Iran playing a constructive role on the sidelines even if it was not a formal participant.
"Now could they contribute from the sidelines? Are their ways for them, conceivably, to weigh in? Can their mission that is already in Geneva ... be there in order to help the process? It may be that there are ways that could happen," Kerry said.
Iran is the main backer, along with Russia, of Syrian President Bashar al-Assad in a conflict that has lasted more than two years, killed more than 120,000 people and uprooted millions more.
The US accuses Iran of providing weapons, manpower and cash, as well as arming members of Lebanese Hezbollah fighting with Assad's forces.
Tehran's participation in the peace talks would likely strengthen any agreement reached in Geneva, and Iran has said it was prepared to take part if invited.
But Washington has opposed Iran's attendance because it has not signed on to a core element of the so-called "Geneva 1" framework.
This says a future Syrian government must be formed by "mutual consent" of the authorities and the opposition, a stance the US says means Assad cannot stay in power.
Syria's main opposition bloc, the National Coalition, has yet to categorically say it will attend the meeting, and warned recently it would not show up if government war planes continued a deadly aerial campaign in northern Aleppo province.
The General Assembly of the Coalition is meeting in Istanbul and on Sunday re-elected Ahmad Jarba as its leader.
Jarba won 65 votes, beating his only rival Riad Hijab - the best-known defector from Assad's regime - by 13 votes.