The Syrian government accused Turkey of breaking its commitments to peace talks as Ankara-backed rebel groups boycotted a third round of meetings due to begin in Kazakhstan on Tuesday.

The Astana talks were launched in January with support from Russia and Iran which back Syrian President Bashar al-Assad, and Turkey, one of the main backers of the opposition.

"When one of the three guarantors breaks their commitment - and I mean Turkey - this means that Turkey must be one that is asked about the non-attendance or participation of these armed groups," Bashar al Ja'afari, the Syrian government envoy, said in broadcast remarks from Astana.

The Syrian opposition said it would not attend the talks because of what it called Russia's unwillingness to end air strikes against civilians and its failure to put pressure on the Syrian army to abide by a widely violated ceasefire.

Ja'afari said the Syrian government had gone to Astana to meet its Iranian and Russian allies, not the armed opposition groups, and "to show the Syrian government's seriousness" in engaging in the Astana process.

Ja'afari said the non-attendance of the armed groups served "the view of the government of Syria and showed the political deficiency of these armed groups". He added that the rebels' decision on whether to attend or not was taken not by them, but by "their operators".