The United States Embassy in Mexico has issued a warning to its citizens about possible clashes between criminal groups and authorities in Sonora and Sinaloa that could break out as a response to the arrest of Rafael Caro Quintero, one of the most wanted drug trafficking leaders in Mexico.

The U.S. government also warned of a possible increase in security in both Sinaloa and Sonora.

In a statement, the embassy reported that, pending the presence of Mexican authorities in both states, its citizens in Mexico must maintain a high level of vigilance and low profile, as well as monitor local media.

Previously, the U.S. government had placed Sonora in a level 3 travel recommendation, under the message of “reconsider the trip due to crime and kidnappings”; meanwhile Sinaloa was classified at level 4.

Mexican authorities detained Rafael Caro Quintero in San Simón, Sinaloa, on July 15. 

He is linked to the 1985 murder of Enrique Camarena, a DEA agent.

During the operation to capture Quintero, a military helicopter crashed near Los Mochis, killing 14 people on board. The cause of the accident has not been disclosed.