Russian Foreign Minister Sergei Lavrov warned there’s a “serious” risk of nuclear war over Ukraine in a statement the U.S. blasted as the “height of irresponsibility.”

“The danger is serious, real. It can’t be underestimated,” Lavrov said in a state TV interview broadcast late Monday. Invoking the Cuban missile crisis of 1962, when the U.S. and the Soviet Union came close to nuclear war, he said that Moscow and Washington had understood the rules of conduct between the superpowers but “now there are few rules left.”

Russia will continue negotiations with Ukrainian President Volodymyr Zelenskiy’s representatives to try to reach a peace agreement, Lavrov said. It would be “useful” to hold discussions with the U.S. too, “but we don’t observe any interest on their part regarding contacts on Ukraine or on other issues.” Both sides have said the talks are at a dead end.