PHNOM PENH (Reuters) - A United Nations body has declared arbitrary the detention of Cambodian opposition leader Kem Sokha, demanding his immediate release and the award of compensation, as the southeast Asian nation prepares for a general election on July 29.

Supporters of Kem Sokha, former opposition leader and ex-president of the now-dissolved Cambodia National Rescue Party (CNRP), hold up a poster near the Appeal Court in Phnom Penh, Cambodia, March 27, 2018. REUTERS/Samrang Pring

Prime Minister Hun Sen, who has ruled the country for 33 years, has waged a campaign against his critics, including the opposition Cambodia National Rescue Party (CNRP), which won the support of a new generation of voters disillusioned at what they see as the corruption and nepotism that have stalked politics.

Kem Sokha, head of the now dissolved CNRP, was arrested in September on charges of treason over accusations of a plot to seize power with the help of the United States, charges denied by both.

In November, the Supreme Court dissolved the CNRP and banned more than 100 of its politicians, in a ruling widely condemned by the international community.

The UN Working Group on Arbitrary Detention (WGAD) called Kem Sokha’s arrest and detention “politically motivated,” amid an “escalating trend in Cambodia of suppression of criticism of the government” ahead of the vote.

“The Working Group considers that Mr Kem Sokha has been deprived of his liberty on discriminatory grounds, namely his political or other opinion,” it said in an April statement seen by Reuters on Wednesday.

The remarks came in response to a complaint by a rights body based in France, the International Federation for Human Rights (FIDH).

“His deprivation of liberty aimed toward, and resulted in, ignoring the equality of human beings, and is therefore arbitrary,” it added.

The U.N. body also urged the Cambodian government to award Kem Sokha compensation for his detention, saying he suffered severe pain from a rotator cuff tear in his shoulder, high blood pressure and hyperglycemia that need urgent medical treatment.

A government official said there was no legal ground for the immediate release of Kem Sokha, however, advising the United Nations not to interfere with the judicial process.

“The UN position should also be made with consideration to the evidence and court hearing,” Huy Vannak, an undersecretary of state at the Interior Ministry, told Reuters.

“Kem Sokha should be encouraged to hire good lawyers to defend his case in court. Doing so will bring justice to him and educate the public about due process and fair trial.”