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Police used cranes to remove concrete slabs and barbed wire barricades on a road leading to the nearby city police headquarters after agreeing to let the protesters into the building.
Government officials did not comment on the developments.
The unexpected reversal of strategy by the government suggests it no longer wants to confront protesters after three days of clashes left at least three people dead and more than 230 injured in street battles.
The protesters who oppose Shinawatra have been besieging various government buildings in the capital, including Government House, the complex that houses her offices.
After days of firing teargas canisters and rubber bullets to hold protesters off, police handed out roses to flag-waving protesters after the barricades were brought down on Tuesday. The protesters mingled with police, shouted slogans and left peacefully.
"We don't want anyone to go inside and ruin government buildings," said Brenda Nong, 51, a protester from Bangkok. "We're good people. We're here for democracy."
The developments raised hopes that the latest eruption of conflict between the Bangkok-based opposition and forces loyal to the prime minister and her brother, former premier Thaksin Shinawatra, may be over.
Shinawatra had said previously that she is willing to do almost anything to end the violence, but cannot accept the opposition's "unconstitutional" demand to hand power to an unelected council.
The protests, determined to topple her government, have renewed fears of prolonged instability in one of Southeast Asia's biggest economies.
"If there's anything I can do to bring peace back to the Thai people, I am happy to do it," the prime minister 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."
Her comments, broadcast in a televised news conference, highlighted the unusual political deadlock Thailand finds itself in.
The protesters, who are mostly middle-class Bangkok supporters of the opposition Democrat Party, accuse the prime minister of being a proxy for her brother. Accused of widespread corruption and abuse of power, he was deposed in a 2006 military coup and lives in exile in Dubai, but remains central to Thailand's political crisis and is a focal point of the protesters' hatred.
Protest leader Suthep Thaugsuban, who met with the prime minister on Sunday night, has said he would not be satisfied with her resignation or new elections. Instead he wants an unelected "people's council" to pick a new prime minister to replace Shinawatra, even though she was elected with an overwhelming majority. His demand has been criticized by many as undemocratic.
However, analyst Thitinan Pongsudhirak told The Associated Press that while Suthep's demands may appear "bold and blatant," they are supported by some who think that the electoral system can never be trusted and want to rewrite the rules and set up their own government.
"I don't know how we can proceed" with Suthep's demand, Prime Minister Shinawatra said at a 12-minute news conference. "We don't know how to make it happen ... I am not against either resignation or dissolution of parliament if this solution will stop the protests ... The government is not trying to cling to power."
Even though Suthep had an arrest warrant against him, he met with Shinawatra on Sunday, with top military leaders present. A second 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.
Schools, offices closed
The protesters' numbers have dwindled from a peak of more than 100,000 a week ago, but hard-core groups have remained at the front lines in running battles with the police. However, by Thailand's bloody standards, the latest round of protests has been marked so far by restraint from security forces.
The police, a force closely aligned with Prime Minister Shinawatra and her brother, have eschewed open street battles with her opponents. In some cases, they were conspicuously absent as protesters raided government buildings and television stations. In others, they have fortified defensively behind barricades.
"The police have learned their lesson from past protests. Yingluck's government must avoid using force while going ahead with criminal proceedings against those who have broken the law," Boonkayiat Karavekphan, a political analyst at Bangkok's Ramkhamhaeng University, told Reuters.
On Monday, many schools and offices, including the United Nations regional headquarters near the Government House, were closed. The French Embassy issued one of the strongest warnings of dozens of foreign governments, urging citizens to stay inside to avoid the conflict on Bangkok's streets.
Political instability has plagued Thailand since the military ousted Thaksin, who remains hugely popular among rural voters. In 2008, 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," Prime Minister Shinawatra said.