Mexican police say they have detained one of the main leaders of a drugs cartel in Apatzingan in the western state of Michoacan.
Thousands of Mexican troops have been patrolling Michoacan state
The arrest of Alfonso Barajas - also known as Ugly Poncho - came after President Felipe Calderon sent 4,000 troops to restore order in the state.
Rival drug-trafficking gangs control parts of Michoacan state and several northern states, correspondents say.
Fighting between them has claimed over 500 lives in the region this year.
Michoacan has become a key air and sea transit point for cocaine, amphetamines and heroin bound for the United States.
Alfonso Barajas - the alleged head of the Gulf drug cartel - leads a team of gunmen, known as the "Zetas", whose job is to fight rival gangs on behalf of the Gulf cartel, police say.
These hired killers include soldiers from the Mexican and Guatemalan armies, Efe news agency reports.
"In this struggle we won't skimp on forces and resources to take on crime and establish minimum conditions of order and authority," Interior Minister Francisco Ramirez told Reuters news agency.
The arrest of Alfonso Barajas comes during a government crackdown on lawlessness and drug-related violence in the region.
Last Monday, President Felipe Calderon ordered thousands of soldiers and state and federal police to patrol the area.
Soldiers also destroyed marijuana and opium plantations.
Correspondents say the move to curb the violence in his home state is President Calderon's first major initiative since his inauguration earlier this month.