BANGKOK (AP) — A firebrand opposition leader vowed Monday to escalate 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 key buildings.

Earlier Monday, Prime Minister Yingluck Shinawatra said she is willing to do anything it takes to end the violent protests but made it clear she cannot accept the opposition’s demand to hand power to an unelected council. Yingluck was elected with an overwhelming majority in 2011, and many observers see the protesters’ demand as unreasonable if not outlandish.

Protest leader Suthep Thaugsuban, center, during a rally in Bangkok in November. Pic: AP.

“Right now we don’t see any way to resolve the problem under the constitution,” she said in the brief 12-minute news conference televised live.

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 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 Monday, protesters commandeered garbage trucks and bulldozers, and tried to ram concrete barriers at the Government House and other key offices. 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. A Bangkok hospital confirmed that two of the people they treated Monday had suffered gunshot wounds, but it is not clear who shot them. The police say they have not used live rounds.

U.N. 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.

In Washington, State Department spokeswoman Jen Psaki said the U.S. was also encouraging restraint and political dialogue. She told reporters that violence and seizure of public or private property “are not acceptable means of resolving political differences.”

The European Union said it was saddened by the violent escalation of previously peaceful demonstrations, and very concerned over occupation of public offices and intimidation of media. “We believe that the response of the Thai authorities has so far been restrained and proportionate,” EU heads of mission in Thailand said in a statement.

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.

“Come and join the people to get rid of the Thaksin regime and we can work together to change Thailand into a pure and democratic country,” said Suthep who has projected his fight as a non-violent campaign for democracy.

Still, he called on his supporters to attack and take over the Bangkok Metropolitan Police headquarters on Tuesday, saying the police were a lackey of Thaksin and Yingluck.

“We’re going to gather all our forces and we’re going to take over the Metropolitan Police Bureau and make it the people’s,” he said.

Monday’s violence took place around key institutions — the Government House, the Parliament and Metropolitan Police Bureau in the historic quarter of the capital. The area has some of Bangkok’s main tourist attractions such as the Grand Palace, Wat Pho temple, the Bangkok zoo, and the backpacker area of Khao San Road. Most of Bangkok, a city of 10 million, has been unaffected.

Analyst Thitinan Pongsudhirak told The Associated Press that while Suthep’s demands may appear “bold and blatant,” they go down well with the people … who think that the electoral system can never be trusted and therefore they have to set up their own government and rewrite the rules.”

The protesters’ numbers have dwindled from a peak of 100,000-plus a week ago but hardcore groups have remained at the frontline, fighting running battles with the police.

In her news conference, Yingluck stuck a conciliatory tone, repeatedly pleading for negotiations, and implied she was willing to hold fresh elections if that helped.

“I am not against either resignation or dissolution of parliament if this solution will stop the protests,” she said. “The government is not trying to cling to power.”

“If there’s anything I can do to bring peace back to the Thai people I am happy to do it,” Yingluck said. “The government is more than willing to have talks, but I myself cannot see a way out of this problem that is within the law and in the constitution.”

She and Suthep met briefly on Sunday in the presence of top military leaders, even though he had an arrest warrant against him. A second arrest warrant was issued Monday on charges of insurrection. His sustained campaign has raised suggestions that he may have the backing of the military, which has long had a powerful influence over Thai politics. The army has often stepped in during times of crisis, carrying out 18 successful or attempted coups since the 1930s.

But this time, if the army does anything, “it will be with great hesitation” because it would have no support internationally and would find it tough to install a new civilian government acceptable to all, said Thitinan, director of Chulalongkorn’s Institute of Security and International Studies.

“So this is something the army wants to avoid. It has stayed on the sidelines for now. And if it does (act), I think we can look at more turmoil down the road, I am afraid,” he said.

Political instability has plagued Thailand since the military ousted Thaksin, who remains hugely popular among rural voters, in 2006. Two years later, anti-Thaksin protesters occupied Bangkok’s two airports for a week after taking over the prime minister’s office for three months, and in 2010 pro-Thaksin protesters occupied downtown Bangkok for weeks in a standoff that ended with parts of the city in flames and more than 90 dead.

“I believe that no one wants to see a repeat of history, where we saw the people suffer and lose their lives,” Yingluck said.