Talks have been rescheduled for Thursday, when the participants will focus on bolstering a shaky ceasefire on the ground.
Talks on the Syrian crisis involving Russia, Iran, and Turkey, that were due to start on Wednesday in the Kazakh capital, Astana, 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 the regime to comply fully with a ceasefire or take any confidence-building steps.
Representatives of Bashar al Assad's regime 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.
Warm-up for Geneva meet
The meeting is viewed as a warm-up for the UN-led negotiations on the protracted war due to begin in Geneva on February 23.
The Syrian regime has confirmed it will be represented again at the Astana talks by its ambassador to the UN, Bashar al-Jaafari.
Russia is sending presidential envoy Alexander Lavrentiev while Iran said it is dispatching Deputy Foreign Minister Hossein Jaberi Ansari.
Agence France-Presse reported that the UN envoy on Syria, Staffan de Mistura, would not participate personally in the latest Astana meeting but that his office would be represented by a "technical team."
The Astana initiative has left the West on the sidelines of the latest push to end the war in Syria.
Moscow has invited the US to participate as an observer but the State Department has yet to confirm Washington will be involved.
Talks are likely to focus on bolstering a shaky ceasefire on the ground after Moscow, Tehran and Ankara agreed to establish a "mechanism" aimed at ensuring the truce.
Russia and Iran have helped turn the tables on the ground with their military backing for Assad, while Turkey and other Gulf nations support rebels fighting to oust the regime.