An international human rights group has called on authorities in Laos to release a prominent rights activists who went missing this month in the country’s capital.

“The Lao government needs to immediately reveal Sombath’s location and release him,” said Brad Adams, Asia’s director of the New York-based Human Rights Watch.

Lao authorities denied they were responsible for the disappearance of Sombath Somphone, who went missing after being stopped by police on Dec 15, and claimed they were unaware of his whereabouts. The Lao Ministry issued a rare statement on Wednesday saying traffic police had stopped Sombath at a checkpoint and unknown men had taken him away, according to Reuters.

“It may be possible Mr. Sombath has been kidnapped perhaps because of a personal conflict or a conflict in business,” the ministry said, adding that they were “seriously investigating” the incident.

The group voiced concern for the 60-year old Ramon Magsaysay Award recipient, described as Asia’s equivalent of the Nobel Prize, for community leadership in 2005. He had worked to promote education and development in the poverty-stricken country.

“Circumstances surrounding the case including security camera footage, indicate Lao authorities took him into custody, raising concerns for his safety,” Human Rights Watch said in a statement.

Arbitrary arrests and detentions run high in the Communist country as part of its heavy crack down on dissent, while police and security force members are suspected of abusing prisoners, according to the US State Department human rights report in 2011.