WASHINGTON — Already testy, relations between the United States and Russia plummeted Monday as Washington suspended diplomatic contacts with Moscow over failed efforts to end the war in Syria and President Vladimir Putin put on hold a deal with the U.S. on disposing weapons-grade plutonium.
On the surface, the suspensions were unrelated. But both underscored deep mistrust and rising tensions between the former Cold War foes, who are increasingly at odds on a number of issues, particularly Syria and Ukraine. In the short term, the end of discussions on Syria deals a potential death blow to efforts to slow the civil war and begin negotiations on possible elections in the country that could mean the ouster of President Bashar Assad.
Underscoring the deterioration between the U.S. and Russia, Putin suspended a deal on plutonium disposal hours before the U.S. announcement. The two powers will still continue discussions on the Iran nuclear deal, Ukraine and other non-Syria issues.
The Russian Foreign Ministry said the U.S. has "done all it could to destroy the atmosphere encouraging cooperation." It cited U.S. sanctions on Moscow over its annexation of the Crimea region of Ukraine and NATO's deployment of forces near Russian borders.
U.S. officials said that despite the suspension of talks with Russia, they would continue to work for a truce and aid deliveries to Syria in other gatherings, including the International Syria Support Group, a collection of nations, including Russia.
The Obama administration said it decided to cut off discussions on Syria because Russia had not lived up to the terms of last month's agreement to restore a tattered cease-fire and ensure sustained deliveries of humanitarian aid to besieged cities, such as Aleppo, which has been under bombardment from Russian and Syrian forces.
White House spokesman Josh Earnest said, "What's clear is that there is nothing more for the United States and Russia to talk about with regard to trying to reach an agreement that would reduce the violence inside of Syria and that's tragic."
"This is not a decision that was taken lightly," State Department spokesman John Kirby said in a statement. "Unfortunately, Russia failed to live up to its own commitments ... and was also either unwilling or unable to ensure Syrian regime adherence to the arrangements to which Moscow agreed."
Kirby's statement said that Russia and Syria are pursuing military action in violation of the cease-fire agreement, and pointed to their targeting of hospitals as well as the Sept. 19 airstrike on a United Nations humanitarian aid convoy. The U.S. accused Russia of bombing that convoy, a charge both Russia and Syria have denied.
Russia intervened on behalf of its close ally Syria on Sept. 30 last year, joining Assad's bombardment of both anti-Assad rebel groups and militant groups such as the Islamic State and Fatah al-Sham Front, an al-Qaida spinoff formerly known as the Nusra Front. Russia is interested in propping up Assad in part because Russia's only naval facility outside the former Soviet Union is on the Syrian coast.
If it had been implemented, the cease-fire deal would have created a joint U.S.-Russian center to coordinate military and intelligence operations. President Barack Obama had overruled Pentagon objections to such cooperation and Secretary of State John Kerry made the offer.
According to a senior U.S. official, the Pentagon has ordered troops who had been deployed to set up the joint implementation center — fewer than 20 — to return to their bases. The official was not authorized to discuss the matter publicly so spoke on condition of anonymity.
The suspension will not affect communications between the two countries aimed at keeping their planes from bumping into each other over Syria.
In Moscow, Russian Foreign Ministry spokeswoman Maria Zakharova voiced regret about the U.S. move and blamed Washington for the failure to persuade the moderate Syrian rebels it backs to cut ties with extremist groups.
"And now, after failing to fulfill the agreements they worked out themselves, they are trying to shift the blame," she said.
The U.S. had agreed to separate the rebel groups but noted it was an extremely slow process. The U.S. has relatively few personnel on the ground in Syria and even the moderate rebels have said they are frustrated with the pace of U.S. help.
Putin's decree on plutonium cited the "emerging threat to strategic stability as a result of U.S. unfriendly actions," as well as Washington's failure to meet its end of the cease-fire deal. It said, however, that Russia will keep the weapons-grade plutonium covered under the agreement away from weapons programs.
Under the agreement, which was expanded in 2006 and 2010, Russia and the U.S. each were to dispose of 34 metric tons of plutonium, enough material for about 17,000 nuclear warheads. When it was signed in 2000, the deal was touted as an example of successful cooperation between Washington and Moscow.
Associated Press Writer Vladimir Isachenkov in Moscow and Lolita C. Baldor in Washington contributed to this report.