The State Department has issued its most serious travel warning yet in light of the coronavirus crisis. On Thursday, it instructed U.S. citizens not to travel internationally.

The Level 4 travel advisory also calls on U.S. citizens who live in the U.S. but are currently overseas to "arrange for immediate return to the United States, unless they are prepared to remain abroad for an indefinite period."

"U.S. citizens who live abroad should avoid all international travel," the warning reads. "If you choose to travel internationally, your travel plans may be severely disrupted, and you may be forced to remain outside of the United States for an indefinite timeframe."

On Saturday, the State Department said that U.S. personnel and their family members who are at high risk if exposed to COVID-19 may return to the U.S. It warned that the decision could limit services for U.S. citizens at some U.S. embassies and consulates.

Many countries have heavily restricted travel across their borders as cases of the coronavirus spread around the world. On Wednesday, President Trump announced that the U.S. is temporarily closing its border with Canada to nonessential traffic.

The European Union has also announced that it is imposing a 30-day entry ban on nonessential travel for non-EU citizens.

Copyright 2020 NPR. To see more, visit https://www.npr.org.