The late king’s body, which had been lying in state at the palace since his death a year ago, was moved to the cremation area on Wednesday night.
The removal of the plaque and the start of a fourth year under military rule marked a bleak chapter in Thailand’s history.
There was no immediate claim of responsibility and security forces said they did not know who was to blame.
Seeking More Power, Thailand’s New King Is Taking the Country Away From Being a Constitutional Monarchy
King Rama X is transforming the nominal powers granted by the constitution into real powers to be exercised at his own discretion, restoring a hybrid form of monarchical rule in the Land of Smiles.
Thailand’s new king, Maha Vajiralongkorn, will pardon a number of inmates, including some jailed under one of the world’s toughest laws against royal insult.