A Cambodian court on Thursday sentenced fugitive opposition leader Sam Rainsy to 10 years in jail for forging and publishing a false map of the border with Vietnam.
A rights group and supporters of Sam Rainsy, who lives in self-imposed exile in Europe, slammed the conviction as politically motivated - a charged denied by the government, which said the map depicted incorrect border markings.
In January, Sam Rainsy, the main rival of Cambodian premier Hun Sen, was already sentenced in absentia to two years in prison over a related conviction for uprooting border posts and inciting racial discrimination.
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Hun Sen maintains close relations with Vietnam's communist regime but Sam Rainsy, 60, whose political party shares his name, has repeatedly accused the government of ceding land to Vietnam.
His new conviction for forging public documents and disseminating false information relates to claims that he posted a "fake map" of the border on his party's website to show Vietnam was encroaching on Cambodian territory.
"The acts of the suspect harm the good relationship between Cambodia and the Socialist Republic of Vietnam," said Ke Sakhorn, president of the judges' panel.
He added that the map was "manipulating" and aimed at "discrediting the government".
Former finance minister Sam Rainsy was also fined five million riel (AU$1,227) and ordered to pay the government compensation of 60 million riel, the court said.
There was a heavy police presence outside the Phnom Penh Municipal Court for fear of protests by supporters of Sam Rainsy, whose party spokesman Yim Sovann said the ruling party was using the court "to slow down the popularity" of the opposition.
"It is a huge setback for democracy in Cambodia," he told AFP.
Ou Virak, chief of the Cambodian Centre for Human Rights, slammed the verdict as "an obvious move by the CPP (the ruling party) to stop Sam Rainsy coming back to compete in the upcoming national elections".
The next polls are due in 2013.
Government spokesman Khieu Kanharith denied the sentence was politically motivated and said Sam Rainsy's own actions were "deeply about politics".
In the January conviction, Sam Rainsy and two villagers were found guilty of intentionally damaging temporary border posts in October last year.
No formal map has yet been agreed between the two countries.
Cambodia and Vietnam officially began demarcating their 1,270-kilometre (790-mile) border in September 2006 after decades of territorial disputes stemming from French colonial times.
