Secretary of State
The warning signaled growing frustration and anger in the Obama administration at what it sees as a widening Russian effort to prop up Syrian President
In a telephone conversation with Russia's foreign minister, Sergey Lavrov, Kerry "expressed grave concern" over the "drastic escalation" of air attacks since the breakdown of a ceasefire last week, State Department spokesman John Kirby said.
In recent days, airstrikes with bunker-buster and incendiary bombs have killed hundreds of civilians in Aleppo, Syria's largest city, and targeted hospitals, water supplies and air raid shelters, U.S. officials say.
In addition to the devastation, desperately needed convoys of food, medicine and other supplies have been blocked to many besieged enclaves because conditions are deemed too dangerous. At least one aid convoy was attacked.
Kerry told Lavrov that "the United States is making preparations to suspend U.S.-Russia bilateral engagement on Syria" unless Russia "takes immediate steps to end the assault on Aleppo and restore the cessation of hostilities," Kirby said in a statement.
Kerry "stressed that the burden remains on Russia to stop this assault and allow humanitarian access to Aleppo and other areas in need," Kirby said.
Asked later if Kerry had set a deadline for action, Kirby said the secretary had "made clear ... the sense of urgency" that was expected in a response from the Russians.
Kirby said Russia's failure to heed the warning would lead to greater chaos in Syria. Extremists will fill the void, he said, and Russia will have to "send its troops home in body bags."
An estimated 250,000 people live in eastern Aleppo, an area that is controlled by rebel forces and has been the chief target of the onslaught by Syrian and government forces and their Russian allies.
Russia and the United States lead an international task force aimed at ending the civil war, and diplomats from Moscow and Washington helped broker a partial ceasefire early this year and again this month. Both efforts soon collapsed.
Kirby said the suspension of cooperation would include the so-called joint implementation center, which was supposed to function as a hub for greater U.S. and Russian cooperation in the war, including shared targeting and intelligence gathering.
The Pentagon privately opposed creation of the joint center.
Moscow has repeatedly ignored Washington's entreaties to stop bombing civilian areas in Syria. Russia says it is targeting terrorists, a claim dismissed by the U.S. government, humanitarian agencies and the Syrian opposition.
Russia strongly supports Assad's government in Damascus and entered the war on his side a year ago, saving it from likely defeat. The Obama administration has called on Assad to step down and is supporting Syrian rebel groups that oppose Islamic State.
During a visit to Cartagena, Colombia, on Monday, Kerry bristled when asked if Russia had "taken the U.S. for a ride" in Syria, as the reporter put it.
"If we hadn't had the conversations we had, there would have been absolutely continued violence and many more people dead," Kerry said, defending the diplomacy.
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