MONTERREY, Mexico, Jan 7 (Reuters) - Mexican troops and police fought a fierce battle with suspected drug hitmen armed with grenades in a town near the U.S. border on Monday, and one police officer was killed, witnesses and Mexican media said.

Soldiers fought around 20 armed men after being attacked with grenades following a search of a suspected drug safe house in Rio Bravo, across the border from McAllen, Texas, witnesses told Reuters.

Mexican media said at least one policeman was killed.

Police confirmed the gun battle in Rio Bravo in the state of Tamaulipas but declined to give more details.

"The aggressors threw dozens of grenades and there was a lot of blood on the street. Some civilians were badly hurt and taken to hospital," said local journalist Ely Enriquez.

Many cities in the border area north of the industrial city of Monterrey are dominated by the powerful Gulf drug cartel and its armed wing, the Zetas.

Suspected drug gunmen killed a local politician in Rio Bravo in November, turning the quiet agricultural town into a flashpoint in President Felipe Calderon's military assault on drug gangs.

Calderon has mobilized some 25,000 troops and federal police to fight powerful organized crime gangs and drug cartels since he came to power a year ago.

He sent 3,000 troops and federal police to Rio Bravo in December following the murder of politician Juan Antonio Guajardo.

In 2007, more than 2,500 people were killed nationwide in drug related murders despite the military clampdown on traffickers. (Reporting by Robin Emmott; Editing by Eric Beech)

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