GENEVA, Switzerland (AP) — A senior Russian diplomat warned Thursday that increasing Western support for Ukraine could trigger an open conflict between nuclear powers.

Speaking at the U.N. conference on disarmament, Russian Deputy Foreign Minister Sergei Ryabkov denounced the U.S. and its allies for openly declaring the goal of defeating Russia in a "hybrid" war, arguing that it violates their obligations under international agreements and is fraught with the war in Ukraine spilling out of control.

Ryabkov warned that "the U.S. and NATO policy of fueling the conflict in Ukraine" and their "increasing involvement in the military confrontation is fraught with a direct military clash of nuclear powers with catastrophic consequences."

He emphasized that Russian President Vladimir Putin's move to suspend the 2010 New START treaty, the last remaining nuclear arms pact with the U.S. came in response to the U.S. and NATO action on Ukraine.

Putin announced the halt in Moscow's participation in New START in his state-of-the-nation address last week. He argued that Moscow can't accept U.S. inspections of Russian nuclear sites envisaged by the pact when Washington and its NATO allies have openly declared Russia's defeat in Ukraine as their goal.

The Russian president noted that Moscow wasn't withdrawing from the pact altogether, and Ryabkov reaffirmed Thursday that Russia would respect the caps on nuclear weapons set under the treaty.

Ryabkov also blamed the U.S. for the failure to ratify the global ban on nuclear weapons and reaffirmed Putin's warning that Moscow would resume nuclear tests if the U.S. does so.

"The U.S. effectively bears responsibility for the fact that the treaty still hasn't come into force more than a quarter century after it was signed," he said, adding that "the U.S. openly demonstrates an intention to resume the tests."

"We can't stand idle," Ryabkov said, noting that if the U.S. conducts a nuclear test, "we will be forced to respond."

"No one should have dangerous illusions that the global strategic parity could be destroyed," Ryabkov added.

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