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.

"The negotiations have been moved to February 16 for technical reasons," a spokeswoman for the Ministry of Foreign Affairs told AFP news agency by telephone without elaboration.

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.

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Kazakhstan, Moscow's close political ally, said last week the two-day talks, to which the UN special envoy for Syria, Staffan de Mistura, had also been invited, would focus on consolidating the Syrian ceasefire.

A new round of UN-backed peace talks is due to begin in Geneva next.

The "closed format" negotiations come after representatives from Damascus and the armed opposition failed to make a breakthrough at indirect talks in the city in January.

The meeting, pushed by key regime-supporter Moscow, is viewed as a warm-up for UN-led negotiations on the protracted war that are due to begin in Geneva on February 23.

While Kazakh officials said they invited both the Syrian government and rebels for the new talks, several of the regime opponents who took part in the previous Astana talks told AFP that they have not received invitations.

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Russia is sending Alexander Lavrentiev, presidential envoy, while Iran said it is dispatching Deputy Foreign Minister Hossein Jaberi Ansari.

De Mistura said he would not participate personally in the latest Astana meeting but that his office would be represented by a "technical team".

Jordan will also be represented by a "high-level delegation" government spokesman Mohamed Momani said.

The Astana initiative has left the West on the sidelines of the latest push to end the war in Syria that has claimed more than 300,000 lives since 2011.

Moscow has invited the United States to participate as an observer but the US Department of State has yet to confirm Washington will be involved.

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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.

The Geneva negotiations are expected to be wider-ranging, focussing on the key issues that divide the government and rebel sides, including the fate of President Bashar al-Assad.

Russia and Iran have helped turn the tables on the ground with their military backing for Assad, while Turkey has supported rebels fighting to oust the leader.