PHNOM PENH (AFP) -- Cambodia's ousted royalist leader Prince Norodom Ranariddh was Tuesday sentenced in absentia to 18 months in jail for fraud, over the illegal sale of his former political party's headquarters.

"There is enough evidence to sentence (the prince) for breach of trust," presiding judge Sao Meach said after the hearing.

Sao Meach said Ranariddh had committed the crime after trying to buy land -- presumably for a new Funcinpec compound -- in his own name using the proceeds from the 3.6-million-dollar sale of the old party headquarters.

He is also guilty of failing to open the land sale up to a competitive bid, the judge said.

Prime Minister Hun Sen said at the weekend that he would not request a royal pardon for the prince, painting his former coalition government partner as an unrepentant troublemaker.

But members of the prince's new political organization, the Norodom Ranariddh Party (NRP), said the verdict was "unacceptable and unjust", and threatened to hold a public protest against the ruling.

"We cannot accept this result, and we will hold a demonstration. The court is unjust," party spokesman Muth Chantha said.

The charges against the prince are at the heart of a battle with his former political allies for royalist support ahead of two key elections.

Cambodians go to the polls next month in local administrative elections, setting supporters say the various criminal complaints against him are politically motivated attempts to prevent defections to his party.

"They intend to keep Prince Ranariddh from coming back to the country -- they are also trying to prevent the Norodom Ranariddh Party from commune elections," he added.

Ranariddh was initially accused of pocketing the money from the sale, with the details of t bulk of the money actually went to the company that is to construct a new Funcinpec headquarters, while the remainder was used to pay for the new land.

An arrest warrant was issued for the prince last month after he twice failed to appear before the court. Ranariddh's lawyer said the prince will not appeal the verdict because he is not likely to get a fair hearing in a higher court. The son of respected former king Norodom Sihanouk, Ranariddh is also under investigation for adultery -- a crime in Cambodia.