A soldier detained on Tuesday for taking part in a protest supporting imprisoned activist Yorm Bopha remained in military police custody last night, his nephew said.

Military police detained Um Nan, 41, a soldier assigned to the Cambodian-Thai border in Preah Vihear province, after he joined the protest near the Supreme Court in Phnom Penh dressed in his soldier’s attire and carrying a United Nations flag.

Nan’s nephew Phan Pheng, 25, a monk at a city pagoda, said yesterday that his uncle had not been charged with an offence but was interrogated at Phnom Penh Military Police Station.

“The authorities have claimed that my uncle’s actions were prohibited by the military,” he said.

Pheng added that his uncle had been suffering from a mental illness and his decision to join the protest was not premeditated.

“My uncle has been experiencing mental problems for two years. The authorities told me he will be released on Thursday,” he said.

National Military Police spokesman Kheng Tito said yesterday that officials had a duty to detain Nan because he had violated military rules by protesting in uniform.

“He broke the law. The law of Royal Cambodian Armed Forces says soldiers must not join political demonstrations,” he said.

Tito declined, however, to say why Nan had been kept overnight rather than sent to a medical facility.

“We had to detain him. But because he has [mental health issues], he won’t have a problem. If he didn’t, he’d have a problem.”

Tito said the man’s commander would provide assistance, which could include sending him to hospital for treatment. It was unclear whether Nan would be granted leave from RCAF.

Am Sam Ath, senior investigator for rights group Licadho, said that if Nan did have the mental health problems his family said, authorities should release him from custody and military service so he could get treatment to ensure his condition did not worsen.

“To keep using a person [in the military] who has a mental problem is a serious human rights violation,” he said. “Many people could be in danger.”

An officer who asked not be named said military police were considering donating money for treatment.

Another family member of Nan’s, Nhem Phan, 55, from Preah Vihear’s Tbeng Meachey district, said the soldier came from a “simple farming family” who couldn’t afford to pay for his treatment.

According to a 2012 report by the Leitner Center for International Law and Justice, Cambodians with mental conditions are often left to their own devices or cared for by family with few resources.

“In the absence of functioning community mental health services, state detention facilities have functioned as de facto holding centres for Cambodians with mental disabilities,” the report reads.

World Health Organization country head Pieter van Maaren said yesterday that a number of hospitals had staff who had received a small amount of training in mental health procedures, but a shortage of specialists remained.

“There is little capacity in Cambodia to provide the kind of services needed for mental illnesses,” he said.