BANGKOK - Anti-government protesters have forced the evacuation of Thailand’s top crime-fighting agency, on the fourth day of street demonstrations.

The marchers, who want the government to step down, targeted a complex of government offices outside the city.

The protest leader said they wanted to shut down government ministries in a bid to cause disruption.

They accuse the government of being controlled by the prime minister’s brother, Thaksin Shinawatra.

The BBC’s Lucy Williamson in Bangkok says the mood of the protesters is very friendly, as they and the government side shadow-box around each other. Prime Minister Yingluck Shinawatra’s secretary general, Suranand Vejjajiva, told the BBC that there were no plans to use the army.

"We are reassured that the police can handle the situation as the protesters are peaceful and do not create any violence,” he said.

The protests are being led by former opposition Democrat Party lawmaker Suthep Thaugsuban, for whom police have issued an arrest warrant.

They began on Sunday and so far have targeted the finance, foreign and interior ministries, among others.

"Let the people go to every ministry that remains to make civil servants stop serving the Thaksin regime,’’ the Associated Press news agency quoted him as saying.

"Once you take over, civil servants can no longer serve the Thaksin regime. Brothers and sisters, go seize the city hall.” Despite the arrest warrant, police made no attempt to detain him as he led protesters to government offices. On Wednesday afternoon, hundreds of protesters surrounded the Department of Special Investigations (DSI), which is Thailand’s equivalent of the US Federal Bureau of Investigation.

The DSI is a particular target for the demonstrators - they accuse its chief of conducting partisan investigations against opponents of the government, says the BBC’s Jonathan Head in Bangkok.

The DSI chief ordered his staff to leave as protesters surrounded the building, Reuters news agency said. However, Mr Suranand said that the government house itself was secure and the government still functioning.

Agencies