The opposition says it will not attend the talks in the Kazakh capital Astana, blaming Russian air strikes and ceasefire violations. The Syrian regime says Turkey has broken its commitment to the talks.
The status of the next round of Syria peace talks in the Kazakhstan capital Astana is unclear as the opposition and regime trade accusations which could delay their start, scheduled for Tuesday.
The Syrian opposition on Monday said it would not attend, blaming Russia for failing to put pressure on Bashar al Assad's regime to abide by a "widely violated ceasefire," and "unwillingness to end air strikes against civilians in rebel-held areas."
"Currently the decision is not to go as a result of Russia continuing its crimes in Syria against civilians and its support of the crimes of the Syrian regime," Osama Abu Zaid, a spokesman for the rebels said, adding that they had informed Turkey of their decision.
The Syrian regime responded on Tuesday, saying Turkey had broken its commitments by not ensuring the attendance of the Syrian 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," said Bashar al Ja'afari, Syrian regime envoy.
Kremlin spokesman Dmitry Peskov called the talks "hugely complex" on Tuesday when asked to comment on the Syrian opposition delegation's decision to not attend.
"We realised from the very beginning that these are hugely complex talks," Peskov said. "The work continues."
The third round of talks in Astana, sponsored by the regime's ally Russia and opposition-backer Turkey, was scheduled to begin on Tuesday, aiming to reinforce a fragile ceasefire deal brokered by Moscow and Ankara in December.
Syrian rebel groups on Saturday called for the postponement of the upcoming round of talks.
They said further meetings would depend on whether the Syrian regime and its allies adhered to a March 7-20 ceasefire.
Russia is backing Syrian leader Bashar al Assad in the conflict, and has launched a diplomatic peace initiative after its air force helped the regime defeat rebels in Aleppo in December, Assad's biggest victory of the six-year war.
The rebels said the regime and its Iranian-backed militia allies were continuing to bombard opposition-held areas near Damascus, Homs, Deraa and Idlib, and preparing to storm two districts on the outskirts of the Syrian capital.
Rebels agree to leave district in Homs
Rebels said an evacuation deal reached on Monday for rebel fighters to leave the opposition-held besieged Homs district of al-Waer dealt a blow to Russia's attempts to portray itself as a credible guarantor of the ceasefire deal.
The evacuation deal was seen as a surrender forced upon rebels after relentless bombing of the heavily populated district by the regime with Moscow's seal of approval.
"It seems Russia invites us to Astana and then imposes forcible displacement of the people of al-Waer ... Moscow has not kept its promises," said Mohammad Alloush, the head of the armed factions' delegations who participated in the past two rounds of Astana talks.
Alloush later confirmed they were not attending, saying Moscow had not kept its promises to stop the bombing of civilian areas or ending displacement of people in rebel pockets near Damascus.
"We want to show the world that the Russians want a political solution that is only in the media. They have to change their policies if they are seeking a solution," Alloush added.