The Biden administration on Tuesday warned that "all areas" of Afghanistan are "unsafe" after an unknown number of Americans were left stranded in the country after the last U.S. troops left on Monday evening, ahead of the Aug. 31 deadline

The State Department issued a Level 4 travel advisory — the most severe travel advisory level — on Tuesday "due to civil unrest, armed conflict, crime, terrorism, kidnapping and COVID-19," an alert on the department's website reads.

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"The Department of State assesses the risk of kidnapping or violence against U.S. citizens in Afghanistan is high," the department said in the alert, noting that the U.S. embassy in Kabul closed all operations Tuesday.

White House press secretary Jen Psaki last week pushed back against reports that Americans were stuck in Afghanistan, calling it "irresponsible to say Americans are stranded."

Various reports published since Monday have indicated that a number of American families and individuals are still stuck in the country after being unable to get on planes in Kabul before the last U.S. troops departed.

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Marine Corps Gen. Kenneth F. McKenzie Jr. said Monday that the last remaining U.S. troops in Kabul have left Afghanistan, likely leaving hundreds of Americans behind.

U.S. Army Major General Chris Donahue, commander of the 82nd Airborne Division, steps on board a transport plane as what the XVIII Airborne Corps calls the last Soldier to leave Kabul, Afghanistan August 30, 2021 in a photograph using night vision optics. XVIII Airborne Corps/Handout via REUTERS.

U.S. Army Major General Chris Donahue, commander of the 82nd Airborne Division, steps on board a transport plane as what the XVIII Airborne Corps calls the last Soldier to leave Kabul, Afghanistan August 30, 2021 in a photograph using night vision optics. XVIII Airborne Corps/Handout via REUTERS. 

"We did not get everybody out that we wanted to get out," McKenzie said.

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The general's comments echoed those of Psaki's from earlier in the day, who acknowledged that there were a "small number" of Americans left in the country.

Psaki did not have a specific estimate for the exact number of Americans left behind, though a senior State Department official placed the total at "below 250."

Fox News' Michael Lee contributed to this report.