Authorities have threatened legal action against those responsible for projecting an anti-government message on landmarks in Bangkok on Sunday night related to the red-shirt street protests in 2010.
The message, "Seeking the truth", was projected on Democracy Monument, Wat Pathum Wanaram and a BTS station.
The same message was projected during the red-shirt demonstrations from April to May 2010 in the capital. The Defence Ministry headquarters was also targeted on Sunday.
Police are now considering what charges can be laid against the culprits.
The Progressive Movement and the Move Forward Party (Kao Klai), the latter of which was formed after the Future Forward Party was disbanded over a loan controversy, claimed responsibility for Sunday's projections.
Both Kao Klai and the Progressives uploaded video footage of the laser projection, with the Progressives claiming responsibility.
"We [the people] are the ones who shined the light of truth," the Progressives said on Facebook, adding it was a teaser of what will come.
"Seeking the truth" is a slogan often used by the United Front for Democracy against Dictatorship (UDD) red shirts during the 2010 protests.
Red shirts took to the streets early that year to oust the Abhisit Vejjajiva government, accusing it of being backed by the armed forces.
The protest ended with a crackdown that saw the deaths of more than 90 people, including state officials.
Prime Minister Prayut Chan-o-cha on Tuesday denounced the laser projection as inappropriate and urged political groups to refrain from activities that would incite public disorder.
Gen Prayut said security forces must investigate the matter, noting the government is focused on managing the economic impact of the Covid-19 outbreak.
Deputy Prime Minister Prawit Wongsuwon said the authorities are investigating whether the projections in Bangkok violated the emergency decree.
Gen Prawit, who served as defence minister in 2010, said the projections were not a form of a symbolic demonstration.
Deputy Defence Minister Chaichan Changmongkol echoed Gen Prawit, saying police will investigate the matter and decide whether those behind the "Seeking the truth" campaign broke any laws.
Deputy Prime Minister Wissanu Krea-ngam declined to comment.
A source at a security agency on Tuesday warned that the Sunday projections were a trap and the government should not fall into it.
The source said police should be allowed to do their job, noting the campaign is aimed at turning public opinion against the government.
The source also compared the projections to the release of the anti-junta rap single Prathet Ku Mee (What My Country's Got) which went viral in 2018.
"It's an old trick like the flash mobs," the source said. "If the government does not treat it carefully, it will become as controversial as Prathet Ku Mee."
The Royal Thai Police's legal office is considering pressing charges such as inciting chaos or unrest, among others," deputy police spokesman Pol Col Krissana Pattanacharoen said.
Col Krissana said security agencies are monitoring the movement and stepping up surveillance on political groups that use this month as a symbol for political activities.
He said, however, the time is too early to summon the people who claimed credit for the projections and police have yet to identify any hidden agenda behind the campaign.
Natcha Boonchai-insawat, spokesman of the Move Forward Party, on Tuesday defended the party's involvement in the "Seeking the truth" campaign, saying it has the right to demand the truth behind the 2010 political violence.
Mr Natcha was reacting to remarks by Thipanant Sirichana, deputy spokesperson of the Palang Pracharath Party, who said his party could face an investigation for allowing an outsider to influence to the group, which could lead to its disbandment.
Meanwhile, UDD leader Nattawut Saikuar said on Tuesday public events to mark the 10th anniversary of the 2010 protests have been put on hold due to the Covid-19 situation, but online talks and discussions will proceed on May 19.
"The conflicts have not gone away over these past 10 years. The NCPO couldn't resolve the divisiveness as it promised when it seized power," Mr Nattawut said.
"The conflicts seem to have deepened and we have started hearing from students," he added.