MEXICO CITY (AP) -- Federal police in Mexico say two Mexican drug cartels have joined forces to destroy a feared gang of hit men along the border with Texas, a shift in allegiances that is fueling drug-war violence.

Intelligence reports indicate the Gulf and La Familia cartels -- formerly bitter rivals -- have formed an alliance to fight the Zetas gang in the Mexican border state of Tamaulipas.

That's according to Ramon Pequeno, the head of the anti-narcotics division of Mexico's federal police.

It was the first official confirmation of the alliance.

The accord has been rumored since banners appeared throughout the region announcing the pact and warning residents not to leave their homes, saying the conflict would get worse.

The campaign to wipe out the Zetas has raised fears of open warfare in Tamaulipas. Armed men are throwing up roadblocks around army garrisons and ambushing military patrols.

Experts say such brazen tactics are meant to get soldiers out of the way of the turf war.

Mexico has deployed tens of thousands of troops to the border and other regions to combat drug trafficking groups.

The effort is backed by U.S. intelligence work and aid. Gang violence has surged despite the three-year-old deployment, claiming more than 18,000 lives since 2006.

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