Mexico drug gang threatens Arizona police

PHOENIX (Reuters) - Police in an Arizona border city are on heightened alert after receiving a warning from a Mexican drug cartel that officers may be targeted if they carry out off-duty drug busts, authorities said on Tuesday.

Nogales Police Chief Jeff Kirkham said the department received the threat through an informant after two off-duty policemen seized 400 pounds (182 kg) of marijuana while horseback riding outside the city in early June.

"The warning was ... that the officers, if they are off duty, are to look the other way and ignore any drug trafficking loads that are coming across the border, otherwise they will be targeted," Kirkham told Reuters.

Arizona straddles a major corridor for Mexican smugglers who haul illegal immigrants and drugs north to the United States in a illicit trade worth billions of dollars a year.

Cartel turf wars and attacks on police have killed more than 25,000 people across Mexico since President Felipe Calderon launched a military crackdown on drug gangs in late 2006.

In recent years, U.S. authorities have become increasingly concerned about drug violence spilling over the border and taking hold in the United States.

Kirkham said he took the threats against Nogales police "very seriously." He said he had asked the Border Patrol for additional support, and had ordered officers to carry communications equipment and guns at all times.

In late April, Arizona passed a tough state law in an effort to stop the state serving as a key corridor for smuggling.

The law, which comes into effect next month, requires state and local police officers to investigate the immigration status of people they reasonably suspect are in the country illegally during a lawful stop.

Critics, including top officials in President Barack Obama's administration, have said it would effectively permit racial profiling and may be unconstitutional.

(Reporting by Tim Gaynor; editing by Jackie Frank)