A plaque in Thailand that commemorated the 1932 coup in the country has gone missing, police in Bangkok said on Saturday, 15 April.

The disappearance of the plaque from a square in central Bangkok has prompted outcry from pro-democracy activists, who believe that its removal is a step by royalist conservatives to rewrite history. Police said they have begun an investigation.

A new plaque that focuses on the importance of the monarchy has now been placed in the square.

"This is another attempt to alter the history of democracy in this country. It is nothing more than fascist rhetoric aimed at brainwashing the next generation," Than Rittiphan, a member of the student-led New Democracy Movement which has protested against military rule, told Reuters.

The tablet was placed in central Bangkok to commemorate the 1932 Thailand coup.

Also known as the Siamese Revolution, the coup ended almost seven centuries of absolute monarchy, Reuters reported.

The Buddhist-majority country has witnessed a succession of political protests and coups for years. The latest coup in Thailand happened in 2014 when military overthrew a democratically- elected government. Thailand is now governed by the junta.

The government of Thailand, led by Prime Minister Prayuth Chan-ocha, who is also a former army chief and staunch royalist, has increased efforts to curb the monarchy's critics under a harsh royal insult law.

The disappearance of plaque came days after the newly-ascended King Maha Vajiralongkorn signed a new constitution in a step to end military rule.

The junta had said that the move by the King would re-establish democracy in the Southeast Asian country. However, critics of the new constitution believe that it would still give the military generals the powers to stay involved in Thai politics.