Leading politician Rodolfo Torre Cantú murdered in Mexico

Gunmen assumed to be linked to Mexico's drug cartels have assassinated a leading politician who was almost certain to win a forthcoming governorship election in the embattled northern state of Tamaulipas, sending shockwaves through national politics.

Rodolfo Torre Cantú was killed alongside at least four members of his entourage when their two vehicles were ambushed yesterday morning, a few miles outside the state capital, Ciudad Victoria. They had been on their way to a rally in the final days of campaigning before Sunday's poll.

"We cannot allow [organised] crime to impose its will and its perverse rules on the decision of citizens and in elections," Felipe Calderón, the Mexican president, said after condemning the attack. Flanked by the minister of defence, the interior minister and the attorney general Calderón called for a united front to, "recuperate Mexico from the hands of crime".

Torre Cantú is by far the highest profile political murder associated with Mexico's escalating drug wars that have killed over 23,000 people since 2007. Nothing remotely equivalent has happened in Mexico since presidential candidate Luis Donaldo Colosio was killed in 1994.

Tamaulipas is among the states hardest hit by the violence, with the death toll accompanied by extortion and generalised terror that ensures most local media no longer even report major gunbattles for fear of angering the gunmen.

The local front is rooted in the rivalry between the old guard leadership of the Gulf cartel and the organisation's erstwhile enforcers known as Los Zetas who have since set up their own independent criminal organisation. The Gulf is said to be allied with trafficking organisations based in other parts of the country, including the Sinaloa cartel, headed by Mexico's most famous trafficker, Joaquín "El Chapo" Guzmán.

Observers say it was an assassination waiting to happen. The turf wars between the drug cartels date back to 2005 but have intensified since Calderón launched a military-led offensive against them in December 2006.

"It is part of the escalation," said former drug tsar Samuel Gonzalez, an implacable critic of the Calderón offensive he believes puts too much emphasis on police and military action instead of rooting out corruption. "If things don't change much more blood will flow."

According to Gonzalez, the assassination of Torre Cantú initially looks like an attempt by the Zetas to remove somebody they perceived as an enemy before he took office as governor. The state government of Tamaulipas has long been accused of collusion with the Gulf cartel.

Torre Cantú belonged to the Institutional Revolutionary party, or PRI, which governed between 1929 and 2000. Since that date the presidency has been in the hands of the National Action party, or PAN, but the PRI still controls the majority of the country's 32 states.Some of the polls leading into the last week of campaigning gave the assassinated 46-year-old candidate as much as a 30 percentage point lead over his nearest rival.

The Tamaulipas electoral authority was due to meet to decide whether to postpone the elections in the wake of the murder.

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