Eight policemen have died in a checkpoint in Sonora, a state on northern Mexico's Pacific coast, during an attack launched by some 30 armed gangsters, officials said Monday.

Those killed included six state police officers and two city policemen from the port city of Culiacan, officials from the state attorney's office (PGJ) were quoted by local newspaper El Universal as saying. Three other police officers suffered life-threatening wounded.

At the time, the policemen were making routine stops at the checkpoint on the Culiacan-Las Brisas Highway, as part of the government's efforts to deploy soldiers and police to search for the killers in the area close to Guamuchil, a nearby city to which witnesses reported the gunmen had fled.

The incident took place a day after the bodies of eight men, all killed in execution style, were found in the state.

Mexico has been carrying out a fierce campaign to crack down on drug traffickers, a war that began in Dec. 2006 within days of Felipe Calderon taking over as president. At least 28,000 people have died since then, according to official data.