Gunmen attack Mexican political candidate, kill 2

MONTERREY, Mexico, June 26 (Reuters) - Suspected drug hitmen attacked a candidate for Mexico's Congress and killed two of his aides, days before the July 5 mid-term election.

Gunmen shot at a vehicle carrying candidate Ernesto Cornejo from Mexico's ruling National Action Party, or PAN, in the town of Benito Juarez in the northern state of Sonora late on Thursday, the state attorney general's office said.

He was unharmed.

The attack was the first time a politician has been directly shot at while campaigning for the congressional vote. Members of the conservative PAN party have denounced threats by drug gangs in northern Mexico.

The PAN's national campaign has focused intensely on President Felipe Calderon army-led crackdown on drug cartels. A string of recent arrests have linked a number of mayors and officials from different parties to trafficking gangs.

The drug war is a major concern for voters and investors as well as a source of anxiety for the United States as gangs fight for dominance of the $40 billion-a-year trafficking trade. It has already damaged foreign investment and tourism.

Sonora is key drug smuggling territory, but Cornejo was not known to have links to cartels.

Calderon has sent thousands of troops across Mexico to try and rein in a cartel war that has killed 12,300 people since he took office in Dec. 2006.

Rural towns are particularly vulnerable as rival cartels seek to control staging posts along smuggling routes to the United States.

Mexico will elect candidates to all 500 seats in the lower house on July 5, along with six state governors and hundreds of mayors. Authorities in northern states are mounting major security operations to prevent attacks at voting booths.