Tonga's Supreme Court

He had 15 charges including bribery, money laundering, perjury and firearms offences.

Lord Tu'ivakano, who was prime minister from 2010 to 2014, has denied the charges and had sought to have them thrown out ahead of a trial.

But Chief Justice Michael Whitten ruled there was sufficient evidence to commit him to trial for all but one of the charges.

One of the seven counts of bribery was thrown out.

Tiuke Mahoni of Ma'ufanga had been charged with possession of methamphetamine and cannabis, as well as attempting to distribute them.

But according to a plea from prosecutors, which was also endorsed by outgoing Attorney General 'Aminiasi Kefu, the 55-year-old is too ill to stand trial.

Justice Charles Cato dismissed the case and Mr Mahoni has returned to the United States to continue treatment.

Meanwhile, two high ranking Customs officials have been arrested on drugs charges and are awaiting trial.

It's the latest blow to Tongasat, a private company Prime Minister 'Akilisi Pohiva has accused a royal princess of using to take millions in public money.

Tongasat had launched an appeal over a Supreme Court decision from August last year, when the Supreme Court ruled $US50 million in payments China made to Tongasat was grant aid intended for Tonga's government.

The company wanted fresh evidence to be heard from four key witnesses, including former finance ministers Lord Matoto and Sunia Fili and former Department of Finance officials 'Aisake Eke and 'Aholotu Palu.