Updated

In the dead of night and without firing a shot, Thailand's military overthrew popularly elected Prime Minister Thaksin Shinawatra on Tuesday after mounting criticism that he had undermined democracy.

The sudden, well-orchestrated coup — a throwback to an unsettled era in Thailand — was likely to spark both enthusiasm and criticism at home and abroad. The military said it would soon return power to a democratic government but did not say when.

Striking when Thaksin was in New York at the U.N. General Assembly, army commander Gen. Sondhi Boonyaratkalin sent tanks and troops into the drizzly, nighttime streets of Bangkok. The military ringed Thaksin's offices, seized control of television stations and declared a provisional authority loyal to the king.

FOXNews.com Reporter's Notebook: Thai Crisis

The coup leaders declared martial law, revoked the constitution and ordered all troops not to leave duty stations without permission from their commanders. The stock exchange was to be closed Wednesday, along with schools, banks and government offices.

Bangkok's normally bustling streets emptied out early Wednesday, from shopping stalls to red light districts, as Thais and tourists learned of the coup.

Across the capital, Thais who trickled out onto barren streets welcomed the surprise turn of events as a necessary climax to months of demands for Thaksin to resign amid allegations of corruption, electoral skullduggery and a worsening Muslim insurgency in the south. Many people were surprised, but few in Bangkok seemed disappointed.

A few dozen people raced over to the prime minister's office to take pictures of tanks surrounding the area. "This is exciting. Someone had to do this. It's the right thing," said Somboon Sukheviriya, 45, software developer snapping pictures of the armored vehicles with his cell phone.

Thaksin recently alienated a segment of the military by claiming senior officers had tried to assassinate him in a failed bombing attempt. He also attempted to remove officers loyal to Sondhi from key positions.

Sondhi, who is known to be close to Thailand's revered constitutional monarch, will serve as acting prime minister, army spokesman Col. Akarat Chitroj said. Sondhi, well-regarded within the military, is a Muslim in this Buddhist-dominated nation.

Sondhi, 59, was selected last year to head the army partly because it was felt he could better deal with a Muslim insurgency in southern Thailand, where 1,700 people have been killed since 2004. Recently, Sondhi urged negotiations with the separatists in contrast to Thaksin's hard-fisted approach. Many analysts have said that with Thaksin in power, peace in the south was unlikely.

In New York, Thaksin declared a state of emergency in an audio statement via a government-owned TV station in Bangkok — a vain attempt to stave off the coup. He later canceled a scheduled address to the U.N. General Assembly.

A Foreign Ministry official, who spoke on condition of anonymity because he was not authorized to speak to the media, said Thaksin tentatively planned to return to Thailand quickly. The official said he could not comment on the possibility of his being arrested if he returned.

Government spokesman Surapong Suebwonglee, who was with Thaksin, said the coup leaders "cannot succeed" and was confident they would fail "because democracy in Thailand has developed to some ... measure of maturity."

However, Sondhi's troops appeared to be in full control and clearly enjoyed the support of the monarch.

Former Prime Minister Chuan Leekpai, a member of the opposition Democrat Party, reflected an ambivalence that is likely to surface in coming days.

"As politicians, we do not support any kind of coup, but during the past five years the government of Thaksin created several conditions that forced the military to stage the coup. Thaksin has caused the crisis in the country," he told The Associated Press.

Thaksin, a telecommunications tycoon turned politician, handily won three general elections since coming to power in 2001 and garnered great support among the rural poor for his populist policies.

But he alienated the urban middle class, intellectuals and pro-democracy activists. They began mass street demonstrations late last year, charging Thaksin with abuse of power, corruption and emasculation of the country's democratic institutions, including what was once one of Asia's freest presses.

Some of Thaksin's critics wanted to jettison his policies promoting privatization, free trade agreements and CEO-style administration.

"I don't agree with the coup, but now that they've done it, I support it because Thaksin has refused to resign from his position," said Sasiprapha Chantawong, a university student. "Allowing Thaksin to carry on will ruin the country more than this. The reputation of the country may be somewhat damaged, but it's better than letting Thaksin stay in power."

He was among hundreds of people gathered at Government House taking photos and video of themselves with the tanks.

Initially, the coup went largely unnoticed in Thailand's popular tourist districts, where foreigners packed bars and cabarets oblivious to the activity about two miles away. But word raced among street vendors hawking T-shirts who packed up their carts quickly and started heading home.

The first sign of the coup came when army-owned TV channel 5 interrupted regular broadcasts with patriotic music and showed pictures of the king. The CNN and BBC signals into Thailand were cut off, preventing the networks from being seen, said Laurie Goldberg, CNN spokeswoman. Later, several hundred soldiers were deployed at government installations and major intersections in Bangkok.

As troops secured key sites in the capital unopposed, the coup leaders declared that a Council of Administrative Reform with King Bhumibol Adulyadej as head of state had seized power in Bangkok and nearby provinces without any resistance. They did not say what reforms the council would carry out.

A senior army general, speaking on condition of anonymity because of the sensitivity of the situation, said the chiefs of the army, navy and air force met with the king to discuss formation of an interim government.

Bhumibol, a 78-year-old constitutional monarch with limited powers, has used his prestige to pressure opposing parties to compromise during political crises. He is credited with helping keep Thailand more stable than many of its Southeast Asian neighbors.

He is the world's longest-serving monarch and celebrated his 60th year on the throne with lavish festivities in June that were attended by royalty from around the world.

The bloodless coup was the first overt military intervention in the Thai political scene since 1991, when an attempt by Prime Minister Suchinda Kraprayoon, a military general, to retain power was countered by street demonstrations and Suchinda's ouster the following year.

Afterward, the military promised to remain in its barracks, in contrast to earlier decades when military coups were a staple of Thai politics.

As recently as March, Sondhi, the army chief and Tuesday's coup leader, sought to ease speculation the military might join the political fray during street demonstrations against Thaksin.

"The army will not get involved in the political conflict. Political troubles should be resolved by politicians," Sondhi said then. "Military coups are a thing of the past."

FOXNews.com Reporter's Notebook: Thai Crisis