BANGKOK (REUTERS) - A political activist from Laos who fled to Thailand has gone missing after seeking refugee status with the United Nations, the latest in a series of disappearances of refugees and asylum-seekers in the region, rights groups said on Friday (Sept 6).

The disappearance of Mr Od Sayavong is suspected to be part of a pattern in South-east Asia, where governments have been accused of working together to arrest and return one another's exiled dissidents.

"Od may be the latest casualty of increased cooperation between the government of Thailand and its regional counterparts to crack down on their respective dissidents in exile," Ms Vanida Thephsouvanh, president of the Lao Movement for Human Rights, said on Friday.

The International Federation for Human Rights called on Thailand to investigate the activist's disappearance. He was last seen on Aug 26.

Mr Sayavong is a member of the "Free Lao", an informal group of Lao migrant workers and activists in Bangkok.

He had been awaiting resettlement to a third country since 2017, when the UN High Commissioner for Refugees (UNHCR) registered him as a person of concern, according to the International Federation for Human Rights.

"The police are ready to investigate the disappearance of Od Sayavong," Mr Krisana Pattanacharoen, a deputy spokesman for Thai police, told Reuters.

"At this time, we have not been informed by relatives or related persons about his disappearance," he added.

The UNHCR could not be reached for comment. Generally, it does not comment on individual cases.

"The international community should strongly condemn this seemingly coordinated form of repression that leads to further shrinking space for civil society in the region," Ms Thephsouvanh said.

Since last year, there have been at least nine cases of South-east Asian governments being accused of either officially arresting, or cooperating in the abduction of, political refugees from other countries in the region.

Several Thai democracy activists who sought refuge in Laos have gone missing over the recent years and two turned up dead in the Mekong River.

When asked about sending back activists, Mr Pattanacharoen said he had no information about that.

In January, Vietnamese blogger Duy Nhat, who had applied for UN refugee status in Bangkok, went missing and was suspected to have been abducted and arbitrarily detained.

Thai immigration authorities said at the time there was no record of Mr Nhat entering Thailand but they were investigating the matter.