MEXICO CITY (Reuters) - Mexican marines may have killed the leader of the brutal Zetas drug gang, Heriberto Lazcano, in a gun battle in northern Mexico, the government said on Monday.

If the death of Lazcano, known as "The Executioner," is confirmed, it would mark one of the biggest victories in President Felipe Calderon's six-year war against drug gangs.

Two alleged gang members were killed in a firefight with Navy troops in the northern state of Coahuila on Sunday and there was "strong evidence" that one of the bodies was Lazcano, the Navy said in a statement.

Lazcano is one of Mexico's most-wanted men and U.S. authorities have offered a reward of up to $5 million for his capture.

The Zetas, considered one of the two most powerful drug gangs in Mexico, have perpetrated some of the most sickening acts seen in the country's drug war.

(Reporting by Michael O'Boyle; Editing by Lisa Shumaker)