Earlier a radical faction of protesters threatened to storm Thailand’s stock exchange and air traffic control if Ms Yingluick did not resign by Wednesday night.

As thousands of protesters continued to occupy parts of Bangkok’s commercial centre Ms Yingluck said it was her duty to protect Thailand’s democracy.

“Democracy belongs to the entire Thai people,” she said.

Protest leader Suthep Thaugsuban, who has been charged with treason but not arrested, has intensified his rhetoric against Ms Yingluck and her democratically-elected government in fiery speeches, saying protesters will close all government offices if the prime minister does not resign within days.

“And if she remains stubborn, we will take custody of the prime minister and all ministers,” he said to a cheering crowd in central Bangkok on Tuesday.

Mr Suthep has also made unsubstantiated claims that Ms Yingluck’s brother Thaksin Shinawatra plans to overthrow the country’s monarchy and create a new state with Mr Thaksin as head.

Mr Thaksin, a billionaire who lives in Dubai to avoid a jail sentence for corruption, has strongly denied any suggestions he is disloyal to widely admired King Bhumibol Adulyadej and for years has been a major donor to royal charities.

Mr Suthep, a former deputy prime minister in a military-backed government, said the first move against Ms Yingluck and her ministers will be to cut water and electricity to their homes.

“I suggest they evacuate their children,” he said.

Police and troops deployed across the city have orders not to intervene against the protesters unless to prevent violence.

The government fears that escalating clashes could prompt an army coup in the country where the military has intervened often in the past.

Under increasing pressure Ms Yingluck has invited leaders of anti-government protesters, political parties, the Election Commission and other state agencies to discuss delaying elections set for February 2.

But Suthep turned down the offer, saying his movement that has brought tens of thousands of people on to the streets would accept nothing more than the resignation of Ms Yingluck’s entire cabinet.

Even the Election Commission refused to take part, saying a large meeting would be unwieldy.

Ms Yingluck’s party has accused the commission “playing politics” and “opposing” the elections.

Protesters accuse Mr Thaksin, a former prime minister ousted in a 2006 coup, of corruptly running the country from abroad, which Ms Yingluck denies.

The two-month crisis is the latest episode in an eight-year conflict that in broad terms pits Bangkok’s middle class and elite with mostly poor rural voters.

Mr Suthep wants to set-up an appointed “people’s council” to run the country to replace the democratic system that has elected Mr Thaksin or his proxies in the past four elections.

Thousands of protesters camping near huge stages set-up at Bangkok intersections say they are prepared to continue their protest in the city of 12 million for days.

But their numbers have thinned since Monday, the first day of what they call operation “shutdown”.

The threat by a student group allied with Mr Suthep’s so-called People’s Democratic Reform Committee to attack the stock exchange and air traffic control prompted alarm among Thailand’s business and tourist industry.

The Stock Exchange said it has prepared to secure the trading system.

Later, Akanat Promphan, a spokesman for Mr Suthep’s committee, said the students had been asked not to carry out the attacks but they reportedly refused to agree.

“We will not lay siege to places that provide services for the general public, including airports, the stock exchange and trains,” Mr Akanat said. “However, we will block government office to stop them functioning.”

Since the unrest broke out in November eight people have been killed and hundreds injured.

There have been a series of drive-by attacks on protest sites by unidentified gunmen.