Mexico has increased security for President Vicente Fox after details of his movements were leaked from inside his own office to drug traffickers.
Police last week arrested Mr Nahum Acosta, the official responsible for organising Fox's visits around the country, for giving information of the president's daily agenda to a gang headed by one of Mexico's top drugs traffickers.
"We have to redouble vigilance because this conflict we have with organised crime has made them challenge the Mexican state," Mr Fox told a radio station yesterday.
More than 100 members of the presidential security service guarded Fox on Sunday when he visited his family's ranch in the central state of Guanajuato, the kind of visit where security is often loose.
The arrest of Mr Acosta raised fears that drug lords may go as far as to try to kill Mr Fox, although security officials said there was no evidence of an assassination plan.
Unlike many of his predecessors who were accused of being lax in the fight against drugs, Fox has led a campaign against narcotics trafficking since he took office in 2000.
The conflict, described by Mr Fox last month as "the mother of all battles," has deepened in recent weeks with a crackdown on jailed traffickers who still run their drug empires from prison.
Last month, drugs gangs executed six prison guards at Matamoros on the US border in revenge for the government's jail crackdown.