(USA TODAY) -- The United States said Monday it was suspending "bilateral" talks with Russia on trying to end the violence in war-torn Syria and claimed Moscow has not lived up to its terms of agreement last month to restore the cease-fire.

"The United States is suspending its participation in bilateral channels with Russia that were established to sustain the cessation of hostilities," State Department spokesman John Kirby said in a statement. "This is not a decision that was taken lightly."

He said the U.S. will also withdraw personnel dispatched to take part in the creation of a U.S.-Russia joint implementation center that was to have coordinated military cooperation and intelligence had the cease-fire taken hold. The suspension, however, will not affect communications between the U.S. and Russia established "to de-conflict counterterrorism operations in Syria."

“Russia and the Syrian regime have chosen to pursue a military course, inconsistent with the Cessation of Hostilities, as demonstrated by their intensified attacks against civilian areas, targeting of critical infrastructure such as hospitals, and preventing humanitarian aid from reaching civilians in need, including through the September 19 attack on a humanitarian aid convoy,” Kirby said.

The U.S. government has accused the Russians and Syrians of intentionally targeting humanitarian aid convoys and medical facilities to break the rebels' resistance. The September airstrike hit a United Nations aid convoy and killed 20 people. Russia and Syria have not taken responsibility for the strike.

The announcement came hours after Russian President Vladimir Putin suspended an agreement with the U.S. on the disposal of weapons-grade plutonium.

In a decree Monday, Putin accused the U.S. of creating "a threat to strategic stability" and Russia said the U.S. failed "to ensure the implementation of its obligations to utilize surplus weapons-grade plutonium," Reuters reported.

Over the weekend, Aleppo, Syria, was hit by dozens of airstrikes as the Syrian government continued a fierce, week-long advance to retake what had been the country's largest city, with a pre-war population of more than 2 million. Several hundred thousand trapped civilians in need of food, water and medicine remain, according to estimates by humanitarian groups.