A former Thai police officer who was fired for gross misconduct as one of the new king's most senior aides was taken to a police station on Thursday to face a charge of building on public land.

Jumpol Manmai's dismissal from the palace was one of the most prominent under King Maha Vajiralongkorn, who has asserted his authority on several fronts since taking the throne in December following the death of his father.

Jumpol looked gaunt and tired as he arrived at the Crime Suppression Division in a grey T-shirt instead of his usual uniform and braid. His head had been shaved - a ritual humiliation for those who fall from grace with the palace.

Jumpol was fired for misconduct described by the palace as "extremely evil". He abused his post for personal gain and his political interests threatened national security, it said.

He does not face charges related to those accusations, but to illegal private building on protected forest land in the northeastern province of Nakhon Ratchasima. Four people are accused alongside him.

Neither Jumpol nor his lawyer made any comment to media.

Speculation in Thailand and on social media over Jumpol's fate and whereabouts in recent days had been fuelled by the deaths in custody in 2015 of two men who had been accused of insulting the palace and abusing links to the monarchy.

Dozens of journalists were at the police station to see Jumpol's arrival.

Jumpol had served as intelligence chief under ousted former Prime Minister Thaksin Shinawatra, whose populist movement's confrontation with a conservative establishment elite has been behind more than a decade of turmoil in Thailand.

One of the most divisive questions in Thai politics is whether Thaksin will be able to return from exile before elections that the junta says will be held next year.

Thaksin, overthrown in 2006, lives abroad to avoid a jail term for corruption charges that he says were politically motivated. His sister, Yingluck Shinawatra, became prime minister after a landslide election win in 2011, but her government was overthrown in the last coup in 2014.

With prison sentences of up to 15 years for any offence of insulting the monarchy, Thais are cautious of commenting on anything related to the palace. The law also limits what news organizations can report from Thailand.