MEXICO CITY (AFP) - A founder of the Zetas, the notorious drug cartel fighting for dominance in northeastern Mexico, has been killed in a clash with the military, a government source said Monday.

Galindo Mellado, known by the alias Z-9, was killed Friday in a gunfight in the northern border city of Reynosa that also left five civilians and a soldier dead, said the source, who asked not to be identified.

Mellado was one of group of elite Mexican soldiers who deserted from the army to work as hired guns for the leader of the Gulf cartel, Osiel Cardenas Guillen.

After Cardenas Guillen's capture in 2003, the Zetas began to operate more independently until they finally broke with the Gulf cartel, unleashing a war for control of its drug trafficking routes in eastern and northeastern Mexico.

The two groups have been locked in a violent struggle for the northern state of Tamaulipas, whose capital Reynosa sits across the border from McAllen, Texas.