MEXICO CITY (Reuters) - Mexican soldiers looking for drug traffickers found $6 million in cash inside a truck near the U.S. border and arrested five men at the scene, the army said on Friday.

Army drug squads in the northern state of Tamaulipas, a smuggling hot spot over the border from Texas, found the U.S. currency stuffed into eight suitcases as they inspected a tractor trailer and smaller truck parked along a highway.

They also found four pistols, the army said in a statement.

Army and federal police units deployed in President Felipe Calderon’s 15-month-old crackdown on drug cartels are grappling with a spike in violence that has left more than 800 people dead in gangland-style killings so far this year.

The U.S.-Mexico border is the main entry point for South American cocaine and other drugs smuggled north to U.S. consumers.

Mexico’s powerful cartels buy masses of U.S. arms and their safe houses brim with cash from their organized crime businesses. Army raids have turned up big hauls of guns and cash since Calderon’s operation began.

Also on Friday, the daily El Universal reported that five soldiers had been arrested for passing information to the Sinaloa alliance of Pacific Coast smugglers.