The West-backed Syrian National Coalition said on Tuesday that it had postponed a vote on attending a peace conference in Switzerland later this month.

It had been expected to decide whether or not to attend the Geneva Two conference on January 22 in Montreux.

But coalition officials said that the vote had been postponed amid sharp disagreement over the issue until at least the middle of next week - less than a week before the conference.

The postponement of a vote of which the outcome is already uncertain adds to doubts about prospects of success at the conference.

Coalition political committee member Hadi al-Bahra said that many members were angry that the administration of President Bashar al-Assad had not agreed to a transitional government.

Mr Assad's government has said he will not surrender power and may run again in elections later this year.

The possibility that Iran, which has strongly backed President Assad, might join the talks has also provoked dissent within the coalition.

Although Iran was not among those invited to the conference by UN secretary-general Ban Ki-moon on Monday, his spokesman has said that Mr Ban favours extending an invitation to Iran.

Syrian National Council member Abdulrahman Alhaj said that disagreement over the talks could split the coalition.

Meanwhile, the Syrian government said that any decision on its attendance of the conference would be determined by a national referendum.