Moscow, Russia - The US Department of State has issued a new travel advisory and warned American citizens in Russia to leave the country "immediately" as the Ukraine conflict continues to escalate.

The US Embassy and Consulates in Russia and the State Department released the alert on Monday, warning Americans of "unpredictable consequences" as a result of the war.

The alert says that US citizens may face limited flights in and out of the country, harassment, detention by Russian government security officials, and even "the possibility of terrorism."

"US citizens residing or travelling in Russia should depart immediately," the embassy said. "Exercise increased caution due to the risk of wrongful detentions."

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The embassy also adds that in September, "the Russian government mobilized citizens to the armed forces in support of its invasion of Ukraine," including those whose dual citizenship was not acknowledged by officials, denying them access to US consular assistance.

Dmitry Peskov, a spokesperson for the Kremlin, reportedly responded to the alert, describing it as "not a new thing."

The US issued similar advisories in the past, but this latest one has been classified as Level 4 – the highest alert level issued by the State Department.

WNBA star player Brittney Griner was notably detained in the country for over 10 months before being exchanged for Russian arms dealer Viktor Bout, and in January, Russia's domestic intelligence service announced a US citizen had been arrested on espionage charges.

February 24 will mark the first anniversary of Russia invading Ukraine under the guise of a "special operation."