Cambodia's self-exiled opposition leader has been fined for defaming a senior member of the country's ruling party, adding to legal woes hurting his party's ability to operate.

The Phnom Penh Municipal Court on Thursday convicted Sam Rainsy, head of the Cambodia National Rescue Party, of defaming Heng Samrin, a legislator and senior member of the Cambodian People's Party.

The court ordered Sam Rainsy to pay 150 million riel ($37,500) compensation to Heng Samrin and a 10 million riel ($2,500) fine. He had claimed that Heng Samrin, while Cambodia's president from 1979 to 1992, accused the country's then-royal leader, Norodom Sihanouk, of being a traitor.

Sam Rainsy has been abroad since mid-November, when an order for his arrest was issued on an old conviction for defaming former foreign minister Hor Namhong.