The US State Department issued a travel advisory on Tuesday warning that Moscow "may single out and detain US citizens in Russia" and repeating earlier warnings for Americans not to travel to the country.

The warning was "due to the unprovoked and unjustified invasion of Ukraine by Russian military forces" as well as the potential for harassment of US citizens by Russian authorities, the travel advisory said, repeating calls for Americans traveling or living in Russia to leave "immediately."

It comes days after a US diplomat was able to visit detained basketball star Brittney Griner, who has been held in Russian custody for more than a month, AFP reported.

Griner, a two-time Olympic gold medalist and WNBA champion, was detained at a Moscow airport on February 17 on charges of carrying vape cartridges that contained cannabis oil in her luggage.

After being apprehended, Griner was immediately placed in a detention center, and last week a Russian court extended her arrest until May 19. She faces up to 10 years in prison.

The arrest came as relations between Moscow and the West hit rock bottom over Russia's invasion of Ukraine.

The administration of US President Joe Biden has led the Western response to the invasion, leveling unprecedented sanctions against Moscow and funneling weapons and aid to Kyiv.