Two bodies that washed ashore a Thailand river in December were the corpses of anti-government activists, police have revealed.

The bodies of the two people — known by the pseudonyms Puchana and Kasalong — were found on Dec. 27 and Dec. 28 on the shore of the Mekong River, wrapped in brown sacks along with blocks of cement.

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The real names of those found was not immediately clear, but officials said they were exiled activists who disappeared from their homes in Laos, where they took shelter after fleeing Thailand.

A third person with whom the two disappeared and worked with, Surachai Danwattananusorn, is a well-known leader of the Red Shirts — an anti-military movement that staged aggressive street protests in Bangkok in 2010 that were violently crushed by the military.

The disappearance of the three has raised concern among fellow activists that they were kidnapped by a death squad -- either vigilantes or officially sanctioned.

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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 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.

At least two other Thai dissidents in Laos have disappeared in recent years, but Thai officials have denied any involvement, and have noted they have tried legal channels to have the suspects extradited.

The Associated Press contributed to this report.