A US admiral pleaded guilty Thursday to lying about his relationship with a Singapore-based defense contractor at the center of a massive bribery scandal that has tarnished top naval officers.

Rear Admiral Robert Gilbeau -- the highest-ranking Navy officer charged in the ongoing probe -- admitted before a federal judge in San Diego that he had lied when he told investigators that he had never received gifts from Leonard Francis, owner of Glenn Defense Marine Asia (GDMA).

Few admirals in the history of the US Navy have ever been convicted of a felony charge.

Gilbeau, 55, told the court that he had misled investigators when he told them he always paid his share when he and Francis dined together about three times a year over a period of several years.

He also admitted that he destroyed documents and deleted computer files when he became aware in September 2013 that Francis and others had been arrested in connection with the fraud and bribery probe.

Gilbeau, who was awarded the Bronze Star and Purple Heart during his 37-year career, is scheduled to be sentenced in the case on August 26.

His attorney David Benowitz told AFP that he would seek probation for his client while prosecutors have agreed to ask the judge that Gilbeau be sentenced to no more than 12 to 18 months in prison.

According to the plea deal, Gilbeau also agreed to pay $50,000 restitution to the Navy and a $100,000 fine. He will also perform 300 hours of community service.

"Of those who wear our nation's uniform in the service of our country, only a select few have been honored to hold the rank of admiral -- and not a single one is above the law," prosecutor Laura Duffy said.

"Admiral Gilbeau lied to federal agents investigating corruption and fraud, and then tried to cover up his deception by destroying documents and files."

- Cuban cigars, Kobe beef -

Francis admitted in January that his company, which provided port services, plied naval officers with cash, prostitutes, Cuban cigars and Kobe beef to ensure US Navy ships stopped at ports where GDMA operated.

The Malaysian businessman earned the nickname "Fat Leonard" in maritime circles because of his girth.

So far, a total of 14 people, including 11 current and former Navy officials, have been charged in connection with the case.

Seven of them have already pleaded guilty and been sentenced to prison terms ranging from 27 months to six and a half years, accompanied by heavy fines.

One of those convicted, US Navy Captain Daniel Dusek, was sentenced in March to 46 months in prison for giving classified information to GDMA in exchange for prostitutes and lavish gifts.

In one instance, according to court records, Dusek arranged for the aircraft carrier USS Abraham Lincoln to stop at a port terminal in Malaysia owned by Francis.

The 2010 port visit cost the United States about $1.6 million, officials said.

As part of his guilty plea, Francis, who is awaiting sentencing, admitted he bilked the US military out of tens of millions of dollars by routinely overbilling for fuel, tugboat services and sewage disposal.

He agreed to forfeit $35 million that he made in the scheme and to repay the navy whatever amount the court decides.

Alex Wisidagama, another GDMA executive who has pleaded guilty in the case, was sentenced in March to five years and three months in prison and ordered to pay $34.8 million in restitution.

During his career in the Navy, Gilbeau was promoted to several top positions, including that of supply officer on the USS Nimitz in 2003-2004, where he was responsible for procuring all goods and services needed to operate the ship.

He also headed the Navy's logistics response to the 2004 tsunami in Southeast Asia.

After being promoted to admiral, he assumed command in August 2010 of the Defense Contract Management Agency International, where he was responsible for critical defense contracts outside the United States.