Alexander Zemlianichenko, Associated Press
Lieutenant General Sergei Rudskoi of the Russian Military General Staff, background center, speaks to the media in Moscow, Russia, Friday, March 18, 2016, while the screen shows an aerial image of an airstrike during the attack of Russian warplanes in Syria.

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

The Russian military has accused the U.S. of dragging its feet on responding to Moscow's proposals on rules for joint monitoring of the Syria cease-fire and response to violations. It said that further delays are leading to civilian casualties.

Lt. Gen. Sergei Rudskoi of the Russian General Staff said in a statement on Monday that if the U.S. fails to respond to its proposals on a joint response, the Russian military will have to start unilaterally using force against those who break the cease-fire, starting Tuesday.

The Russian Foreign Ministry issued a separate but similar statement.

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.

In Geneva, the U.N. special envoy for Syria, whose office is helping monitor cease-fire violations in Syria, said he was "extremely supportive" of U.S. and Russian cooperation to help bolster a peace process for the war-torn country. Staffan de Mistura pointed to the unprecedented "operation center" that is designed to help the two powers' military and civilian experts to "cooperate in containing the crisis."

"The moment that they (the U.S. and Russia) don't talk substantively, we go back to the past," de Mistura said, "and we can't afford it — and they know it too."

The cease-fire that began on Feb. 27, brokered by Russia and the U.S., has helped significantly reduce hostilities for the first time during the five-year conflict that has killed a quarter-million and turned millions into refugees. The Islamic State group and the al-Qaida-linked Nusra Front have been excluded from the truce.

Russian President Vladimir Putin last week recalled some Russian warplanes from Syria, but said the action against those groups will continue.

Keaten reported from Geneva. Vladimir Isachenkov in Moscow contributed to this report.