The Italian and Greek embassies said they had also closed their doors after the unusual U.S. warning, while the French embassy remained open.

South Korea's spy agency says that North Korea has recently supplied additional artillery systems to Russia to support its war efforts against Ukraine.

The number of North Korean troops stationed inside Russia could grow to 100,000, Ukrainian President Volodymyr Zelenskiy said on Tuesday. Kyiv and its Western allies say North Korea has supplied Russia with weaponry and troops to bolster its full-scale invasion of Ukraine.

North Korean leader Kim Jong Un met with the leader of a Russian delegation in Pyongyang and called for deepening trade, economic and scientific ties between the two countries, state media reported Tuesday.

U.S. stock index futures fell on Tuesday as worries about escalating tensions between Russia and Ukraine affected risk sentiment globally, with investors rushing to safe-haven assets. President Vladimir Putin said Russia could consider using nuclear weapons if it was subject to a conventional missile assault supported by a nuclear power,

Escalating tensions between Ukraine and Russia sent investors rushing into safe havens such as gold and Treasurys on Tuesday.