BANGKOK  - Protesters and police observed a temporary truce Wednesday as Thailand prepared to mark the birthday of its revered king, after police had stepped back in a dramatic move to calm violent clashes.

In the day's only significant demonstration, hundreds of protesters descended on the national police headquarters in Bangkok's glitzy downtown shopping district, where police allowed them to cut barbed wire and pull away sections of a concrete barrier. The demonstrators withdrew shortly afterwards.

The prevailing mood was calm in the capital, as demonstrators joined Bangkok authorities to clean up the area around Democracy Monument, where tens of thousands have camped out in more than a month of rallies against the embattled government of Prime Minister Yingluck Shinawatra.

The area is a focus for the celebrations on Thursday for the 86th birthday of King Bhumibol Adulyadej - a date normally observed in a spirit of calm and reverence. Some debris has been cleared at battle-scarred areas around key government buildings, which saw ugly clashes with police earlier in the week as demonstrators tried to storm them.

Several days of street battles abruptly paused Tuesday. Protesters instead handed police flowers after officers said they would no longer use force against demonstrators trying to storm Yingluck's offices as well as the city police headquarters.

The unexpected about-turn followed two days of clashes between stone-throwing mobs and police firing tear gas, water cannon and rubber bullets.

Protest leaders say they have not abandoned their campaign to overthrow Yingluck's administration and curb the political influence of her billionaire brother Thaksin Shinawatra, who was deposed by royalist generals in a coup seven years ago.

They say he still controls the government from exile. Authorities were not worried about the gathering at the police headquarters, said Paradorn Pattanatabut, head of Thailand's National Security Council. "Their movement today is merely to display their power and show that the protests are still continuing," he added.

King Bhumibol, the world's longest-serving monarch, is treated as a near-deity by many and any violence on his birthday would be viewed as a serious sign of disrespect. He has suffered from a range of ailments in recent years. In August he left the Bangkok hospital where he had lived for several years and moved to his palace in the seaside town of Hua Hin with Queen Sirikit.

At the main rally site on Wednesday, protesters began to sweep up rubbish in preparation for the royal festivities.

"We're helping to clean up for the king as it is nearly his birthday," said Palita Nutchoei, 37, wielding a broom at Democracy Monument.

But "we will keep protesting because we feel that we haven't won yet", she added.

The long-running political conflict broadly pits a Bangkok-based elite backed by the military and the palace against rural and working-class voters loyal to Thaksin, a billionaire businessman-turned-populist politician.

The demonstrations, aimed at toppling Yingluck's government and replacing it with an unelected "people's council", are the biggest and most violent since dozens of people were killed in a crackdown on mass pro-Thaksin rallies in Bangkok three years ago.

The current rallies were triggered by an amnesty bill, since abandoned by Yingluck's ruling party, which opponents feared would have allowed Thaksin to return to his home country. He fled in 2008 to avoid jail for a corruption conviction he contends is politically motivated.

Police Wednesday raised the death toll in the clashes to five, confirming the remains of a young man were found on a bus set ablaze in a Bangkok suburb over the weekend.

Protest leader Suthep Thaugsuban, a former deputy premier, said late Tuesday the fight to unseat the government was not over.

"After the king's birthday, we will start fighting again until we achieve our goal," he told AFP, saying victory would only be secured when "Thailand is rid of the Thaksin regime".

An arrest warrant for insurrection was issued for Suthep on Monday and authorities Wednesday called for him to hand himself in.

"I ask Suthep to surrender to police - he has no legitimacy to lead the protest," deputy prime minister and foreign minister Surapong Tovichakchaikul told reporters.