Police in Mexico fight wave of drug-related violence

CULIACAN, Mexico (CNN) - Much of the cocaine and methamphetamines that finds its way to the United States originates or passes through this hot, dusty city in Mexico - one of many front lines in an increasingly violent war between the Mexican government and powerful drug cartels.

Federal officers rumble along city streets, machine guns at the ready. They wear black uniforms and dark visors as they raid suspected safehouses.

The police presence in Culiacan is unfolding in other cities, as well, as authorities combat a wave of drug-related violence.

More than 4,000 people nationwide have died since President Felipe Calderon ordered at least 24,000 troops to join the fight in 2006. More than 1,000 people have been killed this year.