The US Justice Department says it has arrested two alleged leaders of one of Mexico's largest drug cartels. They are suspected of being involved in manufacturing and trafficking the illegal drug fentanyl, which is causing a large number of overdose deaths in the United States.

The department said on Thursday that Ismael Zambada and Joaquin Guzman Lopez were arrested in El Paso in the state of Texas near the Mexican border.

Zambada is known as "El Mayo" and is a co-founder of the Sinaloa Cartel, one of the world's largest drug trafficking organizations. Guzman Lopez is a son of Joaquin "El Chapo" Guzman Loera, the other co-founder.

The two men had already been charged with leading the Sinaloa Cartel's criminal activities in the US and being involved in producing and smuggling fentanyl.

The Justice Department had offered a reward of up to 15 million dollars on Zambada.

The department said in a statement that it "will not rest until every single cartel leader, member and associate responsible for poisoning our communities is held accountable."