An anti-government People's Democratic Reform Committee (PDRC) protester beats an effigy of Prime Minister Yingluck Shinawatra as the surrounding crowd cheers at an encampment in the Pathumwan district, Thursday, Jan. 16, 2014, in Bangkok. Image Credit: AP

Bangkok: Thailand’s anti-corruption authorities launched an investigation against Prime Minister Yingluck Shinawatra on Thursday in a new setback to her government following weeks of mass opposition protests.

The move came as officials pleaded with police to arrest protest leaders who have threatened to take the prime minister and her cabinet ministers captive.

The National Anti-Corruption Commission said its inquiry against Yingluck would probe possible negligence of duty by the premier in connection with a controversial subsidy scheme for rice farmers.

The panel said it would consider whether Yingluck had violated criminal law, but did not say what punishment she could face if found guilty.

The panel will charge 15 other people, including a former commerce minister, with corruption linked to the rice programme, commission spokesman Vicha Mahakun told a news conference.

The scheme has been strongly criticised by Yingluck’s opponents, who have occupied major intersections in the capital since Monday as part of their efforts to force her elected government from office and install an appointed “people’s council” in its place.

The protesters aim to rein in the political dominance of Yingluck’s billionaire brother, fugitive former premier Thaksin Shinawatra, whom they accuse of controlling the government from self-exile.

Critics say the rice programme, designed to shore up Yingluck’s popularity in her party’s northern heartlands, is riddled with corruption and has left the country with a mountain of unsold rice.

Yingluck has called an election for February 2 in an effort to defuse the kingdom’s deepening political crisis but the main opposition Democrat Party is boycotting the polls, which they fear will only return the Shinawatra family to power.

Police said on Thursday the demonstrators’ self-styled “shutdown” of Bangkok appeared to be losing momentum with a dwindling number of protesters on the streets.

The rallies are the latest twist of a political crisis that has gripped Thailand since Yingluck’s brother Thaksin was ousted in a military coup seven years ago.

They were triggered by a failed amnesty bill that could have allowed Thaksin to return without going to jail for a past corruption conviction.

The billionaire tycoon-turned-politician has strong electoral support in northern Thailand, but he is reviled by many southerners, Bangkok’s middle class and members of the royalist establishment.

Yingluck is facing several legal moves, which experts say could potentially bring down her government.

“There’s a war of attrition to wear the Yingluck government down through judicial means and then the anti-Thaksinistas can say it’s part of democracy,” said Paul Chambers, director of research at the Institute of Southeast Asian Affairs at Chiang Mai University in northern Thailand.

Dozens of Yingluck’s MPs already face charges by the National Anti-Corruption Commission in connection with a bid — blocked by the Constitutional Court — to make the upper house fully elected.

If found guilty they could be banned from politics for five years, undermining Yingluck’s chances of forming a new government after the February polls.

Having already temporarily surrounded many key state buildings, demonstrators marched to the government’s revenue department on Thursday.

National Police Chief Adul Saengsingkaew said 7,000 protesters were estimated to remain on the streets on Thursday morning, down from 23,000 the previous evening. Turnout tends to rise when people leave work.

“Many protesters have returned to the south,” Adul said.

Eight people have been killed and hundreds injured in street violence since the protests began more than two months ago. There have been several drive-by shootings by unknown gunmen at the demonstration sites.

The government urged police to detain rally leader Suthep Thaugsuban, who faces an insurrection charge — in theory punishable by death — in connection with the protests.

“It’s the duty of the police to arrest Suthep because he is wanted for insurrection, otherwise police will face malfeasance charges,” Deputy Prime Minister Surapong Tovichakchaikul said after a meeting with the national police chief.

He said Suthep, a former opposition MP, was protected by about 40 personal bodyguards. Some observers believe the veteran political power broker is unlikely to go to jail as he enjoys the support of the kingdom’s royalist establishment.

The opposition heavyweight is also accused by prosecutors of murder linked to a military crackdown on pro-Thaksin opposition protests that left dozens dead when Suthep was deputy premier in 2010.