Russian President Vladimir Putin is believed to boast the world's biggest nuclear arsenal - and has twice warned the West it faces “consequences that you have never encountered in your history” if it intervenes in his invasion of Ukraine. Here, the Express considers which countries could face a nuclear strike if Putin felt threatened.

1) US

Russia's former Cold War adversary could be the most likely target for Russia. The US is believed to hold around 5,600 nuclear weapons, second only to Russia, and Putin recently branded Nato as a US-led military alliance.

Putin said the US was using Nato enlargement in an "aggressive" way to worsen an already delicate global security situation, and before launching his invasion of Ukraine, he complained over the pact's expansion towards Moscow.

A nuclear strike on the US could force Nato allies to reconsider any move against Russia. But the strength of the US nuclear arsenal may deter Russia from launching an attack.

2) UK

Allies of Putin have threatened retaliatory action, with the UK providing significant military aid to Ukraine since the invasion began. Prime Minister Boris Johnson has also personally visited Ukraine President Volodymyr Zelensky to pledge "continued economic and humanitarian support”.

Putin propagandist Dmitry Kiselyov has warned an underwater nuclear strike could see Britain “plunged into the sea”, while Aleksey Zhuravlyov of the Kremlin’s defence committee has said a Russian