The Syrian government said on Monday that the “de-escalation zones” negotiated by Russia, Iran and Turkey, which took effect this weekend, could not be monitored by others, including the United Nations.

The declaration, made by Foreign Minister Walid al-Moallem at a news conference in Damascus, Syria, added to uncertainty over how to ensure compliance with the agreement, which theoretically halts hostilities in four regions of the country.

“We do not accept a role for the United Nations or international forces to monitor the agreement,” Mr. Moallem told reporters. Should there be violations, he said, “the Syrian Army will be prepared to respond in a decisive manner.”

Russia, the main ally of President Bashar al-Assad of Syria and the principal author of the agreement, had suggested when it was announced last week that outside powers could play a monitoring role. But Mr. Moallem’s remarks appeared to rule out that possibility.