By Nate Raymond

NEW YORK (Reuters) - A former Rabobank trader pleaded guilty on Thursday to conspiring to manipulate benchmark interest rates, as U.S. prosecutors dropped separate charges against three ex-ICAP Plc <IAP.L> brokers acquitted in a related British trial.

Paul Thompson, an Australian and former head of money market and derivatives trading in Northeast Asia for the Dutch bank, pleaded guilty in federal court in Manhattan to a single conspiracy count, admitting to scheming to manipulate Libor.

"I apologize to those who were harmed by my actions," he said in court.

The plea came after the U.S. Justice Department in a filing made public on Wednesday dropped charges pending since 2013 against ex-ICAP brokers Darrell Read, Daniel Wilkinson and Colin Goodman after they were acquitted in a British trial in January.

Their acquittals marked a blow to Britain's Serious Fraud Office, which had accused them and three other brokers of conspiring with convicted trader Tom Hayes to manipulate Libor.

Hayes, a former UBS AG [UBSAG.UL] and Citigroup Inc <C.N> trader, was convicted in an earlier British trial in 2015 and is serving an 11-year prison term.

Lawyers for the ex-ICAP brokers did not respond to requests for comment.

Libor, or the London interbank offered rate, underpins trillions of dollars of financial products globally from mortgages to credit cards. The rate is based on what banks say they believe they would pay if they borrowed from other banks.

U.S. and European authorities have been probing whether banks attempted to manipulate the rate to benefit their own trading positions. Investigations have resulted in roughly $9 billion in sanctions worldwide against financial institutions.

The Justice Department had charged 16 people in connection with the investigations, which resulted in settlements by Rabobank and ICAP for $1 billion and $87 million, respectively.

The latest developments in the U.S. cases came as four Barclays bankers were sentenced in London to between 2-3/4 and 6-1/2 years in prison for conspiring to rig Libor.

Thompson, 50, was extradited this week from Australia after being arrested in October while two other ex-Rabobank traders, Anthony Allen and Anthony Conti, were undergoing trial in New York.

Both were convicted in November for conspiring with Thompson from 2006 to 2011 to manipulate the U.S. dollar and yen Libor rates to benefit the bank's trading positions.

In March, Allen was sentenced to two years in prison, while Conti was sentenced to one year. Both are appealing.

The case is U.S. v. Read et al, U.S. District Court, Southern District of New York, No. 13-mj-02224.

(Editing by Chizu Nomiyama and Matthew Lewis)