HOUSTON (Reuters) - Theft of truck loads of green coffee beans is surging in the United States, the world's largest importer of the commodity, as prices for the beans increased to all-time highs in the last year, according to transportation companies.

The issue was discussed by market participants over the weekend in Houston, where the U.S. National Coffee Association held its annual conference.

The U.S. is the world's largest consumer of the beverage. Since coffee is only produced in warmer geographies, it has to import nearly 100% of what it uses and transport millions of bags from ports to roasting plants, mostly via trucks.

"There were dozens of thefts in the last year, something that would happen only rarely in the past," said Todd Costley, logistic sales coordinator for Hartley Transportation, a freight broker in Pembroke, New Hampshire.

Theft of coffee has been reported in producing countries such as Brazil and Vietnam, usually in farms where the beans are temporarily stored after the harvest. Those sites are more vulnerable because they are isolated.

Armed men took 500 bags of coffee worth around $230,000 from a farm in Brazil's Minas Gerais state in January, according to the local police.

In the U.S., the thefts have been done by organized gangs who disguise as transportation companies.

Costley said those fake companies are in the market trying to get small contracts from importers by offering better prices or immediate availability of trucks.

"Importers should be careful about who they hire," he said. "Once they get the coffee, they disappear."

Each truck load has about 44,000 pounds (19,958 kg) of green beans, which at current market value is worth around $180,000.

Some market participants believe the gangs then try to sell the beans to smaller roasters, which are feeling the pain from sky-high prices.

Some importers have started attaching tracking devices to the coffee bags, in an effort to protect their shipments.