Thirteen people including one soldier were killed in a shootout between Mexican security forces and members of the Zetas drug gang near the US border, the Mexican navy said Monday.

"Twelve suspected criminals" and one Mexican marine died in the gun battle late Sunday at Falcon Dam, on the Rio Bravo bordering the US state of Texas, a statement said.

The shootout began after security forces found a suspected Zetas camp during a patrol of an island on the dam, from which they later seized around 20 weapons, the statement said.

The camp served as a transit point for marijuana to be transported by boat to the United States, it added.

The Zetas -- a gang set up by ex-elite soldiers in the 1990s -- are fighting vicious turf battles with their former employers the Gulf cartel in Mexico's northeast Tamaulipas state and nearby regions.

More than 85,000 people took part in a silent protest in Mexico City's main square Sunday to protest rising drug-related violence, according to city officials.

Participants expressed frustration with violence between drug gangs and with security forces that has left some 37,000 people dead since 2006, according to media counts.

They also called for the government of President Felipe Calderon to withdraw some 50,000 troops deployed across the country under a crackdown on the cartels since 2006.