An opposition leader escalated his campaign to topple Thailand's government, and ordered his followers to storm Bangkok's police headquarters after they fought all day with riot police protecting heavily barricaded buildings.

On Monday, Prime Minister Yingluck Shinawatra said she is willing to do anything it takes to end the violent protests but made it clear she would not accept the opposition's demand to hand power to an unelected council during the elections.

"Right now we don't see any way to resolve the problem under the constitution," she said in the 12-minute televised news conference.

Yingluck's comments highlighted the unusual political deadlock Thailand finds itself in with no clear solution in sight.

The standoff intensified as protest leader Suthep Thaugsuban gave a defiant speech late on Monday to thousands of cheering supporters at a government complex they seized last week when the anti-government demonstrations started.

The protests have renewed fears of prolonged instability in Southeast Asia's second-biggest economy and come just ahead of the peak holiday tourist season.

Even if Yingluck dissolves parliament and calls fresh elections, Suthep said, he will "continue the fight... because they can always come back to suck the blood of people, steal from people, disrespect the constitution and make us their slaves."

"If people are happy with elections and go home, I will remain here alone," he said.

Earlier on Monday, protesters commandeered garbage trucks and bulldozers, and tried to ram concrete barriers at the Government House and other key offices.

Hundreds injured

Police repelled them by firing tear gas, water cannons and rubber bullets, as protesters shot back explosives from homemade rocket launchers.

At least three people were killed and more than 200 injured in the past three days of violence, which capped a week of massive street rallies that drew crowds of more than 100,000 at their peak.

UN Secretary-General Ban Ki-moon is "concerned" about the situation in Thailand and urges all sides to exercise "utmost restraint," his spokesman, Martin Nesirky, said.

The protesters, who are mostly middle-class Bangkok supporters of the opposition Democrat Party, accuse Yingluck of being a proxy for her brother, former Prime Minister Thaksin Shinawatra.

He was deposed in a 2006 military coup but remains central to Thailand's political crisis, and is a focal point for the protester's hatred.

The protesters say their goal is to uproot the political machine of Thaksin, who is accused of widespread corruption and abuse of power.

Source: Agencies