BANGKOK (AP) — The United Nations closed its main office in Bangkok, dozens of schools were shut and civil servants skipped work as stone-throwing protesters battled through clouds of tear gas in renewed assaults on key government buildings in the Thai capital on Monday.

The protests aimed at toppling the government of Prime Minister Yingluck Shinawatra have renewed fears of prolonged instability in one of Southeast Asia's biggest economies and come just ahead of the peak holiday tourist season.

After a weekend of chaos in pockets of Bangkok, protesters regrouped outside the heavily-barricaded prime minister's office compound Monday and repeatedly clashed with the police who fired tear gas, water cannons and rubber bullets. Emboldened by their leader's vow to topple Yingluck by Wednesday, they threw rocks at police and tore away sections of barbed wire and concrete barriers. At least three people were killed and 103 injured in skirmishes over the weekend.

In a nationally televised appeal, Yingluck's deputy, Surapong Tovichakchaikul, called on protesters to stop hurting Thailand's image and the economy. Yingluck has not appeared in public since Saturday, and has not been to her office since last week. On Monday, she posted a picture of herself on Facebook in a meeting with senior officials at the national police headquarters.

Using a conciliatory tone, Surapong said "the government will exercise utmost patience and adhere to nonviolent principles."

"The government would like to insist that it will lead Thailand back to peace soon," he said.

The protesters, who are mostly middle-class Bangkok supporters of the opposition Democrat Party, want Yingluck to step down, claiming she is 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, who call themselves the People's Democratic Reform Committee, say their goal is to uproot the political machine of Thaksin, who is accused of widespread corruption and abuse of power.

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Monday's violence took place around key institutions -- the Government House, the Parliament and Metropolitan Police Headquarters 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.

Many of the protesters wore raincoats and plastic bags over their heads, to protect against the sting of tear gas.

In an e-mailed statement to its staff, the United Nations' security department said "there could be violence (Monday) on a large scale ... staff should avoid government offices" and other protest locations. It closed its main office near Government House, which houses several U.N. agencies.

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. The French School is located in a northeastern Bangkok neighborhood where gunshots rang out over the weekend during clashes between Yingluck's supporters and opponents.

It was one of at least 60 schools closed in Bangkok on Monday.

Protest leader Suthep Thaugsuban, a former deputy prime minister, says his aim is to install an unelected "people's council" to select a new prime minister.

Suthep's demand has been criticized by many as undemocratic, and is unlikely to be accepted by a government that was elected with an overwhelming majority.

However, his sustained campaign has led to 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.

Suthep met with Yingluck late Sunday in the presence of top military officials even though he has an arrest warrant against him. He later told cheering supporters that he told Yingluck the only way to end the protests was for her to step down. The military has said it is neutral in the conflict but army commander Gen. Prayuth Chan-ocha has urged the police not to use force.

"There was no negotiation during this meeting," Suthep said. If Yingluck "listens to the people's voices and returns the power to the people obediently, we will treat Ms. Yingluck Shinawatra with politeness because we all are good citizens."

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.

Any further deterioration is likely to scare away investors as well as tourists who come to Thailand by the millions and contribute 10 percent to the $602 billion economy, Southeast Asia's second largest after Indonesia. It is also likely to undermine Thailand's democracy, which had built up in fits and starts interrupted by coups.

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Associated Press writers Papitchaya Boonngok and Raul Gallego Abellan contributed to this report.