Jerusalem - The United States for the first time on Sunday hinted that Iran may be able to play some kind of role at proposed talks to end the war in Syria.
Washington has long opposed calls by Russia and others to allow Tehran to participate in the talks due to be held in Switzerland on 22 January.
It accuses the Islamic republic, the main ally of Damascus, of providing weapons, manpower and cash, as well as arming Hezbollah militants fighting with Syrian President Bashar Assad and allowing him to battle an armed opposition for almost three years.
More than 130 000 people have now been killed in the brutal fighting, with the opposition still splintered and increasingly taken over by hard-line Islamic groups.
US Secretary of State John Kerry, who has been one of the prime movers of bringing together the Syrian regime and the opposition at the talks, stressed Iran could not fully participate without signing up to a June 2012 accord which calls for a transitional Syrian government to replace the current regime.
But Kerry opened the door to some kind of possible involvement by the Iranians in the conference, dubbed Geneva 2.
"Could they contribute from the sidelines? Are there ways, 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 can happen", he said.
"We're happy to have Iran be helpful", he told reporters in Jerusalem.
"Everybody is happy to have Iran be helpful", he added.
Wrangling over the exact make-up of the guest list has been one issue bogging down the holding of the talks, with UN Secretary General Ban Ki-moon due to issue the invitations.
Iran's participation "has to be determined by the secretary general, it has to be determined by Iranian intentions", Kerry said.
The Syria talks come as Iran is also stepping out onto the world stage for the first time in years, involved in discussions to rein in its suspect nuclear programme.
"Iran knows exactly what it has to do with respect to the nuclear programme as well as with respect to Geneva 2 come join the community of nations and do what all of us are committed to doing, which is try to bring about a peaceful resolution in Syria", said Kerry.
The Geneva 2 conference, named because it follows a first peace meeting in the eponymous Swiss city in June 2012, is to be held nearby in Montreux, before moving back to Geneva.
After months of delays, a 22 January date for the talks has been set, but doubts remain about whether the conference will go ahead.
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.