BANGKOK (Reuters) - The Thai army said on Wednesday it had no knowledge of two exiled critics of the military and royal family whose bodies police say were found “stuffed with concrete” along the Mekong River border with Laos.

FILE PHOTO: Former communist and political prisoner Surachai Danwattananusorn gestures during an interview at his home in Bangkok August 25, 2010. REUTERS/Chaiwat Subpransom/Files

Rights groups had expressed concern at the disappearance last year of the two men and another activist in self-imposed exile in Laos, where all three had fled under threat of arrest after the 2014 military coup in Thailand.

DNA tests confirmed the two bodies, which were discovered late last month, belong to Chatcharn Buppawan, 56, and Kraidej Luelert, 46, Thai authorities confirmed on Wednesday.

The two were close aides to political activist Surachai Danwattananusorn, 78, who has been operating online radio programs critical of Thailand’s junta and monarchy from Laos. He also disappeared last month and is still missing.

The police said the cause of their deaths was unknown.

“There are no signs of bullet holes, but there is a wound in their stomach which has been cut open and stuffed with concrete and tied to make it sink. There are also no stab wounds,” Police Major General Thanachart Rodklongtan told Reuters.

The activists’ disappearance from Laos raised concerns among rights groups that critics of the Thai monarchy and army are being targeted in exile.

A military officer, however, dismissed any idea of army involvement in the disappearances.

“This group of people live outside of our area or responsibility, we could not do anything,” Lieutenant General Tharakorn Thamwinthorn, Second Army Region commander, told reporters.

“They are in Laos for many years. We do not know whether they have any problem with people there or not,” he said.

The Thai military seized power in a 2014 coup to end weeks of political turmoil and street demonstrations.

Dozens have fled Thailand since the coup, including cabinet ministers, university professors and political activists. Some have gained asylum in western countries, while the majority live in neighboring Laos and Cambodia.

Many of those had been charged with Thailand’s tough lese-majeste laws, which can carry sentences of up to 15 years imprisonment for defaming, insulting or threatening members of the royal family.

None of these activists has been publicly extradited back to Thailand but at least two other activists have disappeared in Laos, one 2016 and another in 2017, Human Rights Watch said.

“It is clear now that we are in danger,” said Trairong Sinseubpol, 55, another Thai activist in exile. “Things are now very different... Laos doesn’t look that safe now.”