United States authorities have issued a security alert to citizens living in Mexico after the drug cartel leader, Nemesio “El Mencho” Oseguera, who was declared wanted by the U.S., was killed in a military operation in Tapalpa, Jalisco, Mexico, on Sunday.

The U.S. embassy in Mexico issued a security alert on its website, urging its citizens in the country to remain in their homes, “seek shelter and minimise unnecessary movements, and avoid areas around law enforcement activity.”

“Due to ongoing security operations and related road blockages and criminal activity, U.S. citizens in a number of locations in Mexico are urged to shelter in place,” the security alert reads.

It said that all U.S. government officials in some areas of Mexico are to remain at home and work remotely.

“All U.S. government staff at Consulate General Monterrey have been directed to remain in the Monterrey metropolitan area, and U.S. government staff have been directed not to travel to Mazatlan through Wednesday, February 25.

“U.S. government staff in Guadalajara (Jalisco), Puerto Vallarta (Jalisco/Nayarit), Ciudad Guzman (Jalisco), Cancun (Quintana Roo), Playa del Carmen (Quintana Roo), Cozumel (Quintana Roo), Reynosa (Tamaulipas state), Tijuana (Baja California), and Michoacan will shelter in place and work remotely on Monday, February 23, and U.S. citizens should do the same,” the security alert reads.

Mr El Mencho, leader of Mexico’s drug cartel, was killed by the Mexican military, a development that sparked a violent crisis by his gang members.

Before Sunday’s operation, the U.S. had declared El Mencho, who led the Jalisco New Generation Cartel, known as CJNG, wanted, with the State Department placing a $15 million bounty on him.

In February, the President Donald Trump administration designated the CJNG cartel as a foreign terrorist organisation.