Syrian Foreign Minister Walid Muallem said on Monday his country would reject any United Nations role in monitoring the implementation of four "de-escalation" zones.
"We do not accept a role for the United Nations or international forces to monitor the agreement," Muallem told reporters in Damascus.
Regime backers Russia and Iran and rebel supporter Turkey reached a deal on Thursday on four "de-escalation zones" in Syria where the government and opposition will halt hostilities.
The deal says those areas would be bordered by "security zones" with checkpoints and observation centres "ensured by the forces of the guarantors by consensus", but that "third-party" monitors could also be deployed.
Muallem on Monday said there could be a role "as the Russian guarantor has said, for military police", but it was unclear if he was referring to Syrian or foreign units.
The multi-phase plan, signed Thursday in the Kazakh capital Astana, is one of the more ambitious efforts aimed at ending Syria's six-year conflict.
It provides for a ceasefire, rapid deliveries of humanitarian aid and the return of refugees after "de-escalation zones" are created across stretches of eight Syrian provinces.
More than 320,000 people have been killed since Syria's conflict erupted in March 2011.