Russian President Vladimir Putin has delivered a nuclear warning to the West, announcing that Moscow would suspend its participation in the last remaining arms control treaty between Russia and the US.
The New Start treaty aims to reduce the number of nuclear weapons each country has.
Mr Putin said that while he would not withdraw Russia from the treaty completely, he would not allow Nato countries to inspect his country's arsenal.
What is the New Start Treaty?
It caps the number of strategic nuclear warheads that the US and Russia can deploy.
The New Start treaty was signed by US president Barack Obama and Russia's president Dmitry Medvedev in 2010.
It came into force in 2011 and was extended in 2021 for five more years after President Joe Biden took office.
The treaty allows both American and Russian inspectors to ensure that both sides are complying with its terms.
Inspections under the agreement were put on hold in March 2020 because of the Covid-19 pandemic.
Talks on resuming inspections were due to take place in Egypt last November, but Russia postponed them and neither side has set a new date.
Has the treaty been in danger before?
Russia has criticised what it calls a destructive approach to arms control from the US, but even earlier this month, Moscow said it wanted to preserve the treaty.
The US has accused Russia of breaching the treaty, saying Moscow was refusing to allow inspection activities on its territory.
The Russian war in Ukraine has pushed the two countries closer to direct confrontation than at any time in the past 60 years.
Russia and the US account for about 90 per cent of the world's nuclear warheads, and both sides have said that a war between nuclear powers must be avoided at all costs.