Drug traffickers pose a serious threat to Guatemala's general elections in September, President Alvaro Colom said in an interview published Wednesday in Mexico.

Guatemala has stepped up a military clampdown on drug traffickers after 27 farm workers were found decapitated in its northern Peten department in May in a crime blamed on Mexico's Zetas drug gang.

During the elections, drug gangs "will try to recover their influence at a local level, in parliament, in the presidency, at all levels," Colom told Mexico's La Jornada daily.

"I've asked all parties and all candidates to be very careful," Colom said.

"We've put more than 6,400 people with links to drug trafficking in jail ... seven out of 10 members of Guatemalan drug cartels are behind bars ... and they don't like that."

Guatemala will hold elections on September 11 for a new president and vice president, 158 lawmakers, 333 mayors and 20 members of the Central American parliament.

Colom met Mexican President Felipe Calderon in Mexico City Wednesday and signed a string of bilateral deals including on increasing security on their joint border, as well as migration and education.