Russia slammed the United States Monday for delaying the enforcement of a ceasefire in Syria and warned that Moscow might use force against violators unilaterally. The Russia-U.S.-brokered ceasefire began last month with the aim to reduce hostilities in the war-torn region, but excluded the Islamic State group and the al Qaeda-linked Nusra Front from the truce.

The Russian military accused the U.S. of stalling to respond to Moscow's proposals on joint monitoring of the ceasefire, saying it will respond to violators if Washington refuses to coordinate rules of engagement, the Associated Press (AP) reported.

"The delay in the entry into force of the rules agreed upon for responding to violations of the ceasefire in Syria is unacceptable," Lt. Gen. Sergei Rudskoi of the Russian General Staff reportedly said in a statement Monday, accusing Washington of showing "no readiness" to discuss the agreement with Russia.

"The American side was not ready for this particular discussion and for the approval of the agreement," the statement reportedly added.

Last week, Moscow withdrew several of its military contingents in the Middle Eastern country while the United Nations envoy to the Syrian conflict, Staffan de Mistura, resumed his efforts to broker a peace deal between Russia’s close ally Bassar Assad and rebel groups.

Since the civil war in Syria began about five years ago, an estimated 470,000 Syrians have been killed, 7 million people internally displaced and around 4.5 million forced to leave the country.