BANGKOK - Anti-government demonstrators in Thailand said they will step up their protests in an attempt to force Prime Minister Yingluck Shinawatra from office and push through electoral reforms before a general election is held.

The number of protesters camped on the street in the capital has dwindled to about 2,000 over the past week but their leader, former deputy premier Suthep Thaugsuban, called for marches in central Bangkok on Thursday and Friday, followed by a big rally on Sunday.

Anti-government protesters shout slogans during a rally at the Thai Police Headquarters in Bangkok December 18, 2013. Anti-government demonstrators in Thailand said they will step up their protests in an attempt to force Prime Minister Yingluck Shinawatra from office and push through electoral reforms before a general election is held. [Photo/Agencies]

"We will chase Yingluck out this Sunday after she made it clear she will not step down as caretaker prime minister," he said late on Tuesday.

Suthep massed 160,000 protesters around Yingluck's office on December 9, when she called a snap election for February 2 to try to defuse the crisis. Yingluck remains caretaker prime minister.

Suthep has sought the backing of the influential military but has so far been rebuffed. Thailand's military - a frequent actor in Thai politics - ousted Yingluck's brother, the self-exiled Thaksin Shinawatra, when he was premier in 2006.

"We will walk until the number of people who come out to join us outnumber those who elected Yingluck. We will march until the military and civil servants finally join us," Suthep told reporters.

This month, a court issued an arrest warrant for Suthep on the charge of insurrection but police have done nothing to apprehend him, despite his appearance at a seminar with the military and other public events.

On Wednesday, the Department of Special Investigation (DSI), Thailand's equivalent of the U.S. FBI, said it would ask banks to freeze the accounts of 18 rally leaders, including Suthep, to investigate what it called "suspicious activity" - a sign the authorities might be taking a tougher stance.

"We will investigate whether they are funding the protest or if any suspicious transactions have taken place," DSI chief Tarit Pengdith told reporters.

Thailand's eight-year political conflict centres on Thaksin, a former telecommunications tycoon popular among the rural poor because of cheap healthcare and other policies brought in while he was in power.

Yingluck won a landslide victory in 2011 and her Puea Thai Party is well placed to win again because of Thaksin's strong support in the populous, rural north and northeast.

Ranged against him are a royalist establishment, that feels threatened by Thaksin's rise, and, in the past at least, the army. Some academics see him as a corrupt rights abuser, while the middle class resent what they see as their taxes being spent on wasteful populist policies that amount to vote-buying.

Thaksin chose to live in exile after fleeing in 2008 just before being sentenced to jail for abuse of power in a trial that he says was politically motivated.

DEMOCRATS AT ODDS

Even if the election takes place on February 2, its legitimacy could be undermined if the main opposition Democrat Party does not take part.

At a two-day conference that ended on Tuesday, the party reappointed former premier Abhisit Vejjajiva as its leader. However, its members could not agree whether to run in the election or back the street protesters.

Democrat lawmakers resigned from parliament this month to march with Suthep, who was a deputy prime minister in Abhisit's government until 2011.

Some agree with his call for reforms to be implemented before another election is held, but others believe their party, Thailand's oldest, should respect the democratic process and run for office. A decision is expected on Saturday.

Suthep's programme remains vague and it is unclear how long it would take his proposed "people's council" to implement any reforms.

He wants to wipe out vote-buying and electoral fraud and has also promised "forceful laws to eradicate corruption", decentralisation, the end of "superficial populist policies that enable corruption", and the reform of "certain state agencies such as the police force".

Suthep's protest gained impetus in early November after Yingluck's government tried to push through a political amnesty bill that would have allowed Thaksin to return home a free man.