Mexican police have faced a surge of drug-related crime
The head of Mexico's intelligence service has said that drug cartels are threatening the country's democratic institutions, including Congress.
Guillermo Valdes told the Financial Times newspaper that drug traffickers were trying to take over the power of the state.
Gangs have infiltrated police forces, justice departments and government bodies, he said.
Mexico has seen a sharp increase in drug-related violence this year.
Mr Valdes, who is the head of Cisen, the government's intelligence agency, said he could not rule out the possibility that drug money was involved in the campaigns of some members of the national Congress.
"Drug traffickers have become the principal threat because they are trying to take over the power of the state," he told the Financial Times and a small group of foreign media.
The gangs, he said, had grown wealthy from the lucrative drugs trade and had recruited members of police forces, the judiciary and government organisations in order to protect their business.
He said that even federal institutions such as Congress itself could have been targeted by the powerful cartels.
"Congress is not exempt... we do not rule out the possibility that drug money is involved in the campaigns (of some legislators)," he said.
Earlier this month US President George W Bush signed into law a $400m aid package to provide training and equipment for the fight against drug trafficking.
It is believed that only $20m will go to Mr Valdes's service.
Since coming to power in 2006, Mexican President Felipe Calderon has deployed thousands of police and soldiers to tackle drug-trafficking.
There have been an estimated 4,700 drug-related murders during that period.
Mexico has seen a surge in drug-related violence and killings during 2008. On Sunday, eight people, including two youths and a 12-year-old girl, were shot dead when gunmen opened fire on their cars, Mexican officials said.
The attack happened as the victims were waiting at traffic lights in the city of Guamuchil in the state of Sinaloa.
Hours earlier gunmen in Mazatlan, on Sinaloa's coast, killed a policeman and then took dozens of people hostage in a restaurant before escaping.