"The announcement by Russia that it's suspending participation in New Start is deeply unfortunate and irresponsible," said Secretary Blinken.
"We'll be watching carefully to see what Russia actually does. We'll of course make sure that in any event we are postured appropriately for the security of our own country and that of our allies," he added.
The 2010 treaty is the last major US-Russia arms control pact still in force but it has frayed in recent years, with accusations from Washington that Moscow was not complying with it.
"We remain ready to talk about strategic arms limitations at any time with Russia, irrespective of anything else going on in the world or in our relationship," Blinken told reporters at the American embassy in Athens during a regional visit.
He was speaking after Russian President Vladimir Putin announced Moscow's suspension of its participation in the last remaining arms control treaty between the world's two main nuclear powers.
"I am forced to announce today that Russia is suspending its participation in the Strategic Arms Reduction Treaty," said Putin.
Signed by then-U.S. President Barack Obama and his Russian counterpart, Dmitry Medvedev, in 2010, the New START Treaty limited both sides to 1,550 warheads on deployed intercontinental ballistic missiles, submarine ballistic missiles and heavy bombers. Both sides met the central limits by 2018.
However, Russia said Tuesday it will continue observing the restrictions on nuclear warheads imposed by the New START treaty after President Vladimir Putin announced the suspension of Moscow's participation in the arms control pact with the United States.
"Russia intends to adhere to a responsible approach and will continue to strictly comply with the quantitative restrictions on strategic offensive arms stipulated by it (New START) within the life cycle of the treaty," Russia's foreign ministry said in a statement.
Putin claimed, without citing evidence, that some people in Washington were thinking about resuming nuclear testing. Russia's defense ministry and nuclear corporation should therefore be ready to test Russian nuclear weapons if necessary, he said.
"Of course, we will not do this first. But if the United States conducts tests, then we will. No one should have dangerous illusions that global strategic parity can be destroyed," Putin said.
"A week ago, I signed a decree on putting new ground-based strategic systems on combat duty. Are they going to stick their nose in there too, or what?"
It was not immediately clear which ground-based systems had been put on combat duty. Putin said Ukraine had sought to strike a facility deep inside Russia where some of its nuclear bombers are based, a reference to the Engels air base.
In essence, Putin is warning that he can dismantle the architecture of nuclear arms control - including the big powers' moratorium on nuclear testing - unless the West backs off in Ukraine, according to Reuters.
This report was sourced from Reuters and Agence France-Presse.