Dmitry Medvedev, deputy chairman of Russia's Security Council, said that if the New START treaty expired with no replacement then the world should be alarmed that the biggest nuclear powers had no limits for probably the first time since the early 1970s.
The New START treaty, signed in 2010 by US President Barack Obama and Medvedev, who served as Russia's president from 2008 to 2012, limited the number of deployed strategic nuclear warheads to 1,550 on each side.
It is due to expire on February 5 and Russian officials have said they have had no official response from Washington on a proposal from President Vladimir Putin to stick to existing missile and warhead limits for one more year.
"I don't want to say that this immediately means a catastrophe and a nuclear war will begin, but it should still alarm everyone," Medvedev told Reuters, TASS and the WarGonzo Russian war blogger in an interview at his residence outside Moscow.
"The (doomsday) clocks are ticking and they obviously have to speed up," he said.
Medvedev, an arch-hawk, gives a sense of hardliners' thinking within the Russian elite, according to foreign diplomats.
In January, US President Donald Trump indicated he would allow the treaty to expire. "If it expires, it expires," Trump said in an interview with the New York Times. "We'll just do a better agreement."
Arms control treaties, Medvedev said, played a crucial role not just in limiting the number of warheads, but also as a way to verify intentions and to ensure some element of trust between major nuclear powers.
Medvedev, 60, said that for almost his entire life there had been either an arms control treaty or discussions of one between the United States and either the Soviet Union or Russia.
"When there is an agreement, it means there is trust but when there is no agreement, it means that trust has been exhausted," said Medvedev.
In 2023, Putin suspended Moscow's participation in the treaty because of US support for Ukraine in the war with Russia.
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