By Duncan Kennedy
BBC News, Mexico City
Troops get ready for action
The Mexican government is sending thousands of extra troops and police to combat the country's drug cartels.
It follows a series of assassinations of senior police officers in recent weeks, including the acting head of the federal police.
More than 1,000 people have died so far this year in cartel-related violence.
Nearly 3,000 more soldiers and police officers will join the fight against the drug barons, bringing the total to more than 30,000 spread across Mexico.
The new forces are being sent to the state of Sinaloa in the north.
Some infantry troops have already started arriving in Hercules aircraft.
Rise in violence
Sinaloa has been particularly violent in the past few weeks with more deaths and executions and a bigger show of firepower by the drug gangs.
But it is also believed that the Sinaloa cartel hired hit men to kill Mexico's senior federal police officer last week.
Edgar Millan, who had been acting director of the federal police for just 30 days, was shot outside his home in the capital.
He was one of six senior police officers across Mexico to die in the past two weeks.
Mexico's President Felipe Calderon pledged last week to take back the streets from the cartels.
But since he came to office in 2006 more than 3,500 people have died in the violence.
Some government spokesmen have argued that the latest wave of killings is a sign the cartels are being weakened by the massive troop deployment and that they are trying to hit back.
But others say they are still a dangerous force that can adapt to anything, in order to maintain control of a drugs supply to the United States that is said to be worth around $20bn (£10bn).