The United States has unsealed criminal charges against former Cuban President Raul Castro.

Axar.az informs, CNN reports that the charges were unsealed by U.S. authorities as part of a case related to the 1996 downing of two civilian aircraft operated by the Cuban exile group “Brothers to the Rescue,” in which four people were killed, including three U.S. citizens.

According to the indictment, Raul Castro is accused of conspiracy to kill U.S. nationals, destruction of an aircraft, and murder. Prosecutors allege that he was involved in ordering or authorizing the attack while serving as Cuba’s defense minister at the time.

The case marks a significant escalation in already strained relations between the United States and Cuba, and is expected to further heighten long-standing political tensions between the two countries.