A protest site set up near Government House was cleared and 99 demonstrators rounded up in two separate operations at dawn and dusk on Sunday by the Metropolitan Police Bureau (MPB).
The MPB deployed four companies of police to clear the site occupied by two groups of protesters at 6am. However, a number of demonstrators regrouped at 3pm at Chamai Maruchet Bridge near Government House after the police dispersal in the morning.
They demanded the release of the rest of their members and calling for a new constitution to be drawn up, the resignation of the prime minister and the abolition of Section 112 of the Criminal Code -- the lese majeste law.
Pol Maj Gen Piya Tawichai, deputy commissioner of the MPB, said that a total of 99 protesters had been arrested during the two incidents.
He said the 67 arrested in the morning had been taken to the Border Patrol Police Region 1 headquarters in Pathum Thani while the rest who were taken later in the day to the Narcotics Suppression Bureau on Vibhavadi Rangsit Road.
''They would initially be charged with violating the Communicable Disease Control Act and the emergency decree,'' Pol Maj Gen Piya said.
Two monks who joined the protest were apprehended and disrobed at Wat Benjamaborphit near the site, he added.
He said the protest was illegal since the event had trespassed on public property and government offices. The protesters also vandalised a number of fixtures in the vicinity.
Police had received complaints of loud noise and traffic congestion caused by the protest, said Pol Maj Gen Chiraphat Bhumichitr, deputy MPB commissioner.
Half a kilogramme of marijuana and two one-litre bottles of kratom leaf juice were found inside a tent behind the protest stage. Sex toys and condoms were among the items found at the protest site, he said.
The site near Government House had been occupied by two groups of protesters.
The first group was the Save Bang Kloi Coalition of ethnic Karen people from the Kaeng Krachan National Park in Phetchaburi.
They had been entrenched by Government House since early this month demanding justice for ethnic minorities.
The second group comprised members of the Ratsadon group who had marched to Bangkok from Nakhon Ratchasima to make their case for reform.
At the site they call Mu Ban Thalu Fah (Through the Sky Village), the two groups had mingled after the Ratsadon members arrived on March 14 and it had largely become a single anti-establishment protest.
About 6am on Sunday morning, four companies from the Protection and Crowd Control Division police moved in with officers using loudspeakers to order everyone to pack up their belongings and leave the area in three minutes.
The protesters pleaded for more time to pack up their belongings but were removed as threatened before ordnance disposal and forensic police arrived to sweep the site.
At 3pm, several protesters returned to Chamai Maruchet Bridge near Government House and held a live music performance where they were vociferous in the criticism of the police's earlier handling of their dispersal.
Then later, around 5.30pm, crowd control police moved in and closed traffic at Misakawan and Nang Loeng intersections as protesters spilled onto the street parading banners with anti-government messages.
At 6pm, police issued a second ultimatum, giving all those present 15 minutes to vacate the area or face legal action.
A large proportion of the group refused and twenty minutes later the police swooped in from Phitsanulok Road and Wat Benchamabophit to arrest 32, many of whom were holding pictures of their leaders who are being held by authorities without bail.
Among those apprehended was Chinnawat Chankrachang, leader of a protest group in Nonthaburi. No violence was reported.
Yingcheep Atchanont, manager of the Internet Law Reform Dialogue and a protest leader, urged everyone to go home ahead of fresh rallies in coming days.
The Facebook page Unme of Anarchy of the Ban Thalu Fah protesters later posted a message reaffirming their constitutional right to free speech and insisted they had complied with the law by notifying the authorities of their demonstration in advance.
Meanwhile, the United Front of Thammasat and Demonstration said in a Facebook post they would converge on Government House to reclaim the protest site and denounce the illegitimate arrests.
The Feminist Liberate group also spoke out on the seizure of condoms and sex toys accusing the army of misrepresenting props that were being used to call for sexual equality and sexual health awareness in an adjoining protest calling for the revocation of Section 287 to pave the way for the legalisation of sex toys in Thailand.