Mexican President Vicente Fox has boosted his personal security after reports that an adviser leaked details of his travel plans to a drug cartel.
Mr Fox said the cartels had managed to penetrate the Mexican government at the highest levels, but that he would not let the traffickers defeat the state.
Nahum Acosta, a senior member of the team organising Mr Fox's official trips, was arrested last Thursday.
There has recently been a surge in drug-related killings in Mexico.
The authorities suspect druglords of organising the violence from behind bars.
'Extra vigilance'
Mr Fox ordered increased security at police stations and government departments, adding that the problem had reached the level of the presidency.
"We have to redouble vigilance because this conflict we have with organised crime has made them challenge the Mexican state," he told Mexican radio.
Correspondents say Mr Fox has been praised by Washington for taking on powerful drug cartels. He launched a fresh campaign against organised crime last month.
He has put the police and army in control of prisons from where they believe drug gang leaders have been organising attacks.
Security officials say there is no evidence of a plan to assassinate Mr Fox, but there are fears that he may be targeted.
Mr Acosta, who has been working for the president since 2001, is alleged to have passed information to a drug smuggler close to fugitive trafficker Joaquin "El Chapo" Guzman.
Local newspapers reported that the aide had been recorded on video meeting a leading trafficker in Mexico City.
A judge has ordered Mr Acosta to remain in police custody, but he has not been formally charged.
There is no evidence that other members of Mr Fox's staff are involved in the alleged leak.
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