Syria's government warned bluntly that fighting terrorism is its priority, dismissing the Western-backed opposition and any attempts at outside intervention.

Foreign Minister Walid al-Moallem's comments put into perspective the previous day's efforts by the opposition Syrian National Coalition (SNC) to deride the government's position.

United Nations mediator Lakhdar Brahimi had said he would meet both sides separately in Geneva a day after a testy opening to UN-sponsored peace talks.

But Mr Moallem, who is in Switzerland, said the SNC did not represent the opposition and efforts toward a political resolution to three years of fighting were premature.

The priority was "to fight terrorism. This would pave the way for the start of the political process," he said.

After a hostile start to the talks, the UN was taking a day to see if there was enough common ground between President Bashar Assad's government and the SNC to allow for direct talks for the first time since the rebellion began in 2011.

High-level mediation has yielded little so far, but Mr Brahimi said there were signs the sides might be willing to bend on humanitarian aid, ceasefires and prisoner exchanges.

Meanwhile, Iranian President Hassan Rouhani called for new Syrian elections, saying his nation would respect the results.

"The best solution is to organise a free and fair election in Syria" and once the ballots are cast "we should all accept" the outcome, he said.