The United States Embassy has told Americans in Russia to leave the country immediately while outbound flights remain available.

In a security alert on its website Sunday, the U.S. Embassy in Russia warned Americans to flee the country due to the continued cancelation of commercial flights.

“An increasing number of airlines are canceling flights into and out of Russia, and numerous countries have closed their airspace to Russian airlines,” the alert said. “U.S. citizens should consider departing Russia immediately via commercial options still available.”

The U.S. Embassy further reminded Americans in the country that the Department of State’s Travel Advisory has set Russia at “Level 4: Do Not Travel.”

“Do not travel to Russia due to ongoing tension along the border with Ukraine, the potential for harassment against U.S. citizens, the embassy’s limited ability to assist U.S. citizens in Russia, COVID-19 and related entry restrictions, terrorism, harassment by Russian government security officials, and the arbitrary enforcement of local law,” the travel advisory states.

For Americans still in Russia, the U.S. Embassy recommended the following actions:

Following Russia’s invasion of Ukraine last week, commercial flights to and from the country have been canceled by Western powers.

“Flights that are in Russian airspace will leave it shortly,” Lufthansa said in a statement. “Lufthansa Group continues to monitor the situation closely and is in close exchange with national and international authorities.”

Likewise, the Hungarian discount airline Wizz Air said that it has been trying to evacuate crews from Ukraine since the invasion.

“We are still working hard to get them out at the earliest opportunity,” Wizz Air spokeswoman Christie Rawlings said in a statement. “We are in regular contact with all of the crew and can confirm that many of them have been able to get out of the country via ground transport. The majority of our employees based there are Ukrainian nationals.”

KLM Royal Dutch Airlines told CNBC that it will be cutting some commercial flights to Russia. British officials also banned the Russian carrier Aeroflot from landing in the United Kingdom. Other airlines have simply rerouted planes around the conflict zone, with United Parcel Service flying south around Ukraine last week.

“While this alternate routing adds additional time to the flight, we feel this is a viable alternative to continue to provide safe and efficient operations,” the airline told pilots. “We will continue to monitor the situation and provide additional updates to you when we receive them.”