The Russian Foreign Ministry expresses "deep disappointment" about the move

International efforts to end the fighting in Syria have been dealt a serious blow, with the United States suspending direct contacts with Russia on halting the war, and chilly relations turned even frostier after Russia put a hold on a plutonium disposal deal with Washington.

The two decisions, announced in their respective capitals just hours apart on Monday, were ostensibly unrelated but 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.