Talks on the Syrian crisis involving Russia, Iran, and Turkey that were due to start in the Kazakh capital, Astana, on Wednesday have been delayed by one day, Kazakhstan's foreign ministry said without explaining the reason for the delay.
Syrian rebels cast doubt on Monday over whether they would attend the talks, accusing Russia of failing to get Damascus to comply fully with a ceasefire or take any confidence-building steps.
Kazakhstan, Moscow's close political ally, said last week the two-day talks, to which United Nations special envoy for Syria, Staffan de Mistura, had also been invited, would focus on consolidating the Syrian ceasefire.
Delegations of the Damascus government and the rebels attended the previous round of talks in Astana in January but refused to negotiate directly with each other or sign any documents.
A new round of UN-backed peace talks is due to begin in Geneva next week.