Russia on Monday warned the United States that it will start responding to cease-fire violations in Syria unilaterally starting Tuesday if the U.S. refuses to coordinate rules of engagement against the violators. A U.S. official contended the issues were being discussed "in a constructive manner."

The Russian military have accused the U.S. of dragging its feet on responding to Moscow's proposals on joint monitoring of a Syria cease-fire. A top Russian general said on the weekend that further delays are leading to civilian casualties, like in Aleppo where 67 civilians reportedly have been killed by militant fire since the truce started.

Lt. Gen. Sergei Rudskoi of the Russian General Staff said in a statement on Monday that Russia will have to use force unilaterally that because the U.S., in talks with Russia last week, had refused to coordinate a joint response.

"The American side was not ready for this particular discussion and for the approval of the agreement," the statement quoted him as saying.

But in a statement e-mailed to The Associated Press, a U.S. official in Geneva said: "We have seen the media reports on alleged Russian concerns over cease-fire violations. Whoever is making such statements must be misinformed, because these issues have been discussed at length already, and continue to be discussed, in a constructive manner."

The official demanded anonymity because he was not authorized to speak publicly on the matter.

The cease-fire that began on Feb. 27, brokered by Russia and the U.S., has helped significantly reduce hostilities. The Islamic State group and the Al Qaeda-linked Nusra Front have been excluded from the truce.

Russian President Vladimir Putin last week recalled some of Russian warplanes from Syria, but said the action against the Islamic State group and the Al Qaeda-linked Nusra Front will continue.