One tonne of drug discovered in frozen carcasses on container ship as officials face gang wars over supply routes to US

The lengths to which drug smugglers will go to conceal their consignments was revealed when the Mexican navy said it had seized more than a tonne of cocaine stuffed inside frozen shark carcasses.

Masked naval officers cut open more than 20 carcasses filled with slabs of cocaine after checking a cargo ship in a container port in the state of Yucatan. X-ray machines and sniffer drugs led them to the stash.

"We are talking about more than a tonne of cocaine that was inside the ship," said navy commander Eduardo Villa yesterday . "Those in charge of the shipment said it was a conserving agent but after checks we confirmed it was cocaine."

Drug gangs tapping the lucrative US market have been forced to come up with more imaginative methods of getting drugs to North America such as in sealed beer cans, religious statues and furniture, in the face of a crackdown by the Mexican military.

President Felipe Calderon has tasked 45,000 troops and federal police with crushing the powerful smuggling cartels responsible for a surge in violence across the country that has spilled over into US states such as Arizona, creating concern in Washington.

At a remote mountaintop site in the northern state of Sinaloa yesterday, the Mexican navy showed reporters one of the largest methamphetamine labs ever found in the country with enough ephedrine to produce more than 40 tonnes of the drug, estimated to be worth $1.4bn (£900,000). But despite the efforts of government forces the gangs remain strong. Some 2,750 people have died in drug violence in Mexico this year, a rate similar to last year, when 6,300 were killed.

Led by Mexico's most wanted man, Joaquin "Shorty" Guzman, smugglers from the Pacific state of Sinaloa are fighting a turf war with rivals over smuggling routes into the US.