The U.S. Embassy is urging any Americans who are in Russia to "depart immediately" over concerns that they could be harassed and singled out by Vladimir Putin's government. The embassy published a notice on Sunday saying that U.S. citizens in Russia should "exercise increased caution due to the risk of wrongful detentions."

The updated travel advisory – which has remained at the highest level, "do not travel," since October – came just days after the White House announced that President Biden will travel to nearby Poland on Feb. 20, ahead of the one-year anniversary of Russia's full-scale invasion of Ukraine. John Kirby, spokesperson for the National Security Council, said the nation is concerned Putin's attacks on Ukraine could "get more vicious" as spring approaches.

In the latest advisory, the U.S. Embassy said that there are "unpredictable consequences" of Russia's assault, including "the potential for harassment and the singling out of U.S. citizens for detention by Russian government security officials." There is also the possibility that U.S. citizens could be forced to fight in the war.

"In September, the Russian government mobilized citizens to the armed forces in support of its invasion of Ukraine," the travel advisory says, referencing the partial mobilization that Russia said called up about 300,000 reservists to fight in the country's invasion.

"Russia may refuse to acknowledge dual nationals' U.S. citizenship, deny their access to U.S. consular assistance, subject them to mobilization, prevent their departure from Russia, and/or conscript them."

Vadym Skibitskyi, a representative of Ukraine's military intelligence, told The Wall Street Journal that Russia is "preparing for the second wave of mobilization."

"Everything is ready," Skibitsky said. "The personnel is in place, the lists are ready, the people tasked with carrying out recruitment and training are on standby."

Some U.S. citizens have already been subject to harassment and unfair treatment, the U.S. said, and have been convicted "in secret trials or without presenting credible evidence." American citizens in Russia who are engaged in religious activities have also had "questionable" criminal investigations opened against them, and recently, the Russian government has expanded its ability to detain and arrest people for engaging with foreign entities, discrediting the country or its military and advocating for LGBTQ+ rights, the U.S. said.

Because of the ongoing situation. the embassy said the U.S. government will be "severely limited" in its ability to help American citizens in Russia. And it may be difficult for U.S. citizens to leave as the situation worsens, as U.S. credit and debit cards don't work in Russia and sanctions have limited the ability to electronically transfer funds, the embassy said. Commercial flight operations are also "extremely limited," officials said, and could be difficult to acquire with short notice.

Those who choose to stay or who have not yet determined a way to leave have essentially been advised to lay low and avoid contentious areas.

CBS