Here are some key facts about the treaty signed by former US president Barack Obama in 2010:

- 2010 'reset' -

The accord signed in the Czech capital Prague in 2010 by Obama and then Russian president Dmitry Medvedev was part of Obama's push to "reset" ties with the Kremlin.

Obama's successor Donald Trump was hesitant to extend it, saying that any nuclear treaty must also include China, whose arsenal is rapidly growing.

On taking office President Joe Biden extended it by five years until 2026, with his administration noting that the treaty was meant "to make the world safer."

- 30 percent fewer warheads -

The accord restricts the former Cold War rivals to a maximum of 1,550 deployed warheads each, a cut of about 30 percent from a limit set in 2002, and 800 launchers and bombers -- still enough to blow up the world many times over.

The treaty also provides for a series of mutual onsite inspections, a cornerstone of former US president Ronald Reagan's "trust but verify" arms control mantra.

- Ukraine 'toxicity' -

Russia's invasion of Ukraine a year ago dealt a severe blow to the treaty, with Putin issuing thinly veiled threats to use nuclear weapons and the US leading the push to arm Ukraine and punish Moscow for its aggression.

Moscow announced in August 2022 that it was suspending US inspections of its military sites, claiming that the United States was obstructing visits of its facilities, which Washington denied.

Russia also indefinitely postponed talks under the treaty that had been due to take place in Cairo, accusing the United States of "toxicity and animosity".

In January, the United States accused Russia of being in non-compliance with the treaty.

Russia's ambassador to the United States replied that Moscow had been "irreproachably observing" the accord and that the responsibility for the escalation lay "entirely with Washington".

- The last pact -

The New START pact is the last post-Cold War arms control deal remaining between Moscow and Washington.

In 2019 the two powers ripped up the landmark 1989 Intermediate-Range Nuclear Forces (INF) treaty concluded by Reagan and Soviet leader Mikhail Gorbachev, which limited the use of medium-range missiles, both conventional and nuclear.

A year later, Trump also pulled the US out of the "Open Skies" treaty, which allows unarmed surveillance flights over participating countries in Europe, the former Soviet Union and North America.

Trump accused Russia of repeated violations of the treaty, which Moscow denied.

Russia also later withdrew from the deal.

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