BANGKOK — DNA tests show that two bodies found washed up on the shore of the Mekong River in Thailand's northeast are the corpses of anti-government activists, police said Tuesday, in what are feared to be political killings.

The two, known by the pseudonyms Puchana and Kasalong, were among three exiled activists who disappeared in December from homes in Laos, where they took shelter after fleeing Thailand. There is a group of Thai exiles in Laos associated with the anti-military Red Shirt movement that staged aggressive street protests in Bangkok in 2010 that were violently crushed by the military.

Several members of a hard-core faction advocating that the kingdom of Thailand become a republic are wanted in their homeland on charges of lese majeste, or insulting the monarchy, a serious crime punishable by up to 15 years in prison per offense.

The disappearance of the three has raised concern among fellow activists that they were kidnapped by a death squad, either vigilantes or officially sanctioned. Thailand's military announced after taking power in a 2014 coup that defending the monarchy would be a priority. However, disappearances and assassinations of political dissidents have mostly been sporadic since the 1970s, when politicians and farmer and labor leaders were targeted to remove a popular democracy after demonstrations ousted a military dictatorship in 1973.

The Nakhon Phanom provincial police chief, Pol. Maj. Gen. Thanachart Rodklongton, said forensics lab results matched the bodies' DNA to samples from family members.

The bodies were found on Dec. 27 and Dec. 28 wrapped in brown sacks along with blocks of cement, presumably to weigh them down.

The real names of the two have not been made public, but the third person with whom they worked who also went missing is a well-known Red Shirt leader and long-time dissident, Surachai Danwattananusorn, better known as Surachai sae Dan. His fate is unknown. Now in his seventies, he has spent many years in prison on lese majeste and other charges since the 1970s, when he was a communist guerrilla in southern Thailand.

The three had not seen by friends in Laos since the middle of December.

Since 2016, at least two other Thai dissidents in Laos have disappeared under suspicious circumstances.

Thai officials deny any involvement in the disappearances, and note they have tried legal channels to have the suspects extradited.

While some Thai dissidents have managed to obtain political asylum in Western countries, others who lack connections, documentation and funds are stuck in the neighboring countries of Laos and Cambodia. Some have tried to keep doing political work over the internet, while others prefer to keep a low profile. All live in limbo because of the transactional nature of Thailand's relations with its neighbors, who might regard it advantageous to hand over the fugitives.