Troops have been deployed since December 2006 against drug gangs
Mexican troops have arrested seven suspected members of a drug cartel hit squad over the torture and murder of a retired general in Cancun last week.
Among those detained was Octavio Almanza, the alleged head in Cancun of Los Zetas, a hit squad working for the powerful Gulf Cartel, officials said.
Retired general Mauro Enrique Tello was killed along with two other men.
Gen Tello had just been hired by the local government to help root out corruption in the resort city.
Mr Almanza, a former soldier, is suspected of orchestrating the murder of Gen Tello, an army lieutenant and a civilian, whose bullet-riddled bodies were found in a car on 3 February.
Mr Almanza is suspected of being the Cancun leader of Los Zetas, a group of ex-soldiers aligned with drug-traffickers, officials said.
Prosecutors are also investigating whether the local police chief, Francisco Velasco, used his position to protect and collaborate with the hit men.
He was arrested on Monday when troops swooped on a police building in Cancun.
"Cancun is one of the chief destinations for cocaine arriving from Central and South America," defence department official Brig Gen Luis Arturo Oliver told reporters as he announced the latest arrests.
Some 5,400 people were killed in drug-related violence in Mexico in 2008, as criminal gangs fight federal forces deployed against them and battle each other for control of drug-trafficking routes to the US.