BANGKOK (AFP) - A well-known high-ranking Thai police officer who disappeared from the public sphere four months ago has been charged with malfeasance, the police said on Saturday (Feb 20), the latest twist in a shadowy purge of planners behind a birthday parade for the queen.

Former police spokesman Prawut Thavornsiri was a familiar face who appeared on daily television broadcasts with updates on high-profile criminal cases, including the bombing in Bangkok last year that killed 20 people.

He suddenly vacated his post in late last October during a probe into another policeman and two others accused of exploiting their connections to the monarchy to profit off "Bike for Mom" - a massive cycling event that celebrated Queen Sirikit's birthday in August.

Those men were charged with defaming the royal family, a broadly interpreted crime that carries a 15-year jail sentence in a country where palace intrigue is shrouded in secrecy and rumour.

Two of those jailed over the event were later found dead in their prison cells within weeks of each other last November, according to the police, a string of events that shocked the public.

On Saturday, deputy police chief Sriwarah Rangsitpramkul said Prawut, who has not been seen in public since the purge, had also been charged for his involvement in the cycling event, which was led by the 63-year-old Crown Prince.

The former spokesman will be prosecuted for installing antennas on a Bangkok building that were used in connection with the event, he said, without elaborating on what the radio transmitters were used for.

He also confirmed that Prawut had not returned to Thailand.

"General Prawut Thavornsiri, former national police spokesman, is currently not in the kingdom but it will not affect our summoning him to hear the charges of malfeasance," said Mr Sriwarah.

"Bike for Mom", which was followed by a similar fanfare for the king last December dubbed "Bike for Dad", saw Prince Maha Vajiralongkorn lead tens of thousands of cyclists through the streets of the capital to celebrate his parents' birthdays.

The tightly choreographed events threw the Crown Prince into the limelight at a time of heightened concern over the health of his revered father - 88-year-old King Bhumibol Adulyadej.

The widely venerated King's ailing health is seen as an exacerbating factor behind the country's decade of political turmoil, which has been pierced by two military coups.

The military has long styled itself as protector of the monarchy.