Participants of Syria peace talks attend a meeting in Astana, Kazakhstan January 23, 2017.

Kazakhstan said Tuesday that a new round of Astana talks on the Syria conflict led by Russia, Turkey and Iran will take place behind closed doors, as the make-up of any rebel delegation remained unclear.

The “closed format” negotiations are set to start Wednesday in the Kazakh capital some three weeks after representatives from Damascus and the armed opposition failed to make a breakthrough at indirect talks in the city.

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.

Damascus has confirmed it will be represented again 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.

UN envoy on Syria Staffan 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 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 President Bashar al-Assad, while Turkey has supported rebels fighting to oust the strongman.