BOGOTA (Reuters) - Colombian authorities will impound trucks blocking highways and double the number of security forces patrolling roads, President Juan Manuel Santos said on Thursday, as a 38-day-long truckers strike continues to spark violent protests.

The strike, which began in early June, has caused sharp rises in food prices, clogged ports and hit exports of the country's high-quality arabica coffee.

Negotiations between the truckers union and the government are at a stalemate, as the workers demand a rise in cargo prices and cuts to motor fuel and road toll costs.

One person has been killed in clashes, and the governor of Boyaca province was injured in a highway accident that authorities blamed on the protesters.

Trucks blocking highways will now be impounded, and drivers or truck owners participating in violent protests will have their licenses revoked and could face fines of up to 480 million pesos ($163,458), Santos said in a televised address. The number of soldiers and police patrolling roads will double to 50,000.

"There is not and will not be any tolerance on the part of the government when faced with illegal behavior," Santos said, adding that the government was willing to come to a "realistic" agreement with the union.

"If we accept the proposals on the table, family food costs would go up 10 percent," the president said. "The government cannot allow, and I will not allow, that food costs for things like eggs, meat and rice rise permanently."

The union could not immediately be reached for comment.

Some products have been moved in small protected caravans, the president said, and the government will temporarily approve private cars for transport of cargo.

Coffee, the country's premier agricultural export, has been hit hard by the protests.

Growers are already struggling because of a drought caused by the El Nino weather phenomenon and bracing for coming heavy rains, but the strike may send exports plunging by half in July, the coffee federation told Reuters this week.

High food prices have helped push 12-month inflation to 8.60 percent through June, more than double the central bank's 2 percent to 4 percent target range. ($1 = 2,936.53 Colombia pesos)

(Reporting by Julia Symmes Cobb and Nelson Bocanegra; Editing by Lisa Von Ahn)