ASTANA, Kazakhstan—The Syrian regime and the rebel opposition ended the first day of peace talks on Monday without reaching agreement on how to monitor a shaky cease-fire, but the sides continued trying to hammer out details of a potential deal.

The indirect negotiations in the capital of Kazakhstan are expected to conclude on Tuesday and it is not clear if any agreement will emerge. The talks that Russia and Turkey had initially hoped would begin mapping out a political settlement to the six-year conflict got off to a rocky start amid harsh rhetoric.

Expectations for the talks have been tempered in recent days as both sides have said the cease-fire, which was meant to be the foundation for a peace deal, was not being adhered to.

Russia’s special envoy to the talks, Alexander Lavrentyev, said Monday’s talks were “quite successful” and said participants were working on a statement that they hoped to publish Tuesday, according to Russian news agencies.