His disappearance coincides with a deadly wave of violence against politicians along the country's northern border.

The Mexican newspaper El Universal quoted federal sources as saying that Cevallos had been kidnapped, but a federal prosecutor's spokeswoman said she could not confirm that.

Powerful figure

Arsenio Duran, the attorney-general for Queretaro state, told a local radio that investigators found blood stains inside the car and a pair of eyeglasses, a pen and a pair of scissors that relatives said Cevallos often carried with him.

Duran also said a night watchman had told police that he was supposed to arrive to his ranch in the town of Pedro Escobedo on Friday night but he never made it.

Cevallos, 69, continued to be an influential political figure, as well as one of Mexico's most successful attorneys.

He emerged from relative obscurity during Mexico's first televised debate by presidential candidates in 1994, striking a chord with the middle class with his calls to topple the Institutional Revolutionary Party, which had held power since 1929.

He finished second to Ernesto Zedillo that year, but his party finally won the presidency six years later when Vicente Fox was elected.

Felipe Calderon, the president, said in a statement he had ordered federal authorities to help Querataro state's investigators in the search for Cevallos, calling him "a key politician in the Mexican transition to democracy".

Blood found

Franc Contreras, Al Jazeera's correspondent in Mexico City, said: "Mexican investigators are scouring Querataro state just north of Mexico City. Thay are digging through the evidence left behind in the vehicle of this very powerful man in Mexico.

"Investigators tell Al Jazeera that blood was found inside the vehicle. There is evidence that a scuffle, some sort of violence took place."

Cevallos is a very powerful figure in the ruling party and is said to have been a mentor to Calderon during his political ascendancy.

"This man has also served as a powerful lawyer, including on a number of controversial cases lately. One of those having to do with land rights in a northern state where drug violence is taking place, the border state of Tamaulipas.

"So there is suspicion that the case could be linked to any dealings he could have had in that part of Mexico."

Meanwhile, at least eight people have been killed and 20 others wounded by armed men in a bar in northern Mexico.

The killings took place in Torreon near the US border.

More than 22,000 people have died in drug violence since Calderon launched a war on drug cartels more than three years ago.