SAN JOSE, Costa Rica, July 9 (Reuters) - Costa Rican authorities seized almost two tonnes of cocaine on two speed boats on Monday, the latest capture in a series of large, U.S.-backed drug operations in the Central American country.

Costa Rican coast guards hauled 899 kilograms of cocaine off one boat along the country's Pacific coast and stopped another with a similar amount with help of the U.S. Coast Guard.

Authorities have yet to disclose the exact amount on the second boat as Colombian smugglers sabotaged the vessel and caused it to sink in shallow waters, slowing the narcotics collection.

"Judging by the size of the quantity on the first boat, we expect to find a similar amount on the boat that sank," said Public Security Minister Fernando Berrocal.

The Costa Rican and U.S. Coast Guards had been searching for the boats after being alerted by U.S. authorities on Saturday evening, Berrocal said.

Traffickers have changed tactics, hugging the Costa Rican coastline in order to avoid detection on the high seas by the U.S. Coast Guard, he added.

The Coast Rican government, with U.S. assistance, has captured 21 tonnes of cocaine this year, compared with 23 tonnes in all of last year.

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