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

The sudden, well-orchestrated coup — the first in 15 years and 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.

In his first public appearance since seizing power, Sondhi Wednesday asked for the public's support and declared the coup was necessary to end serious conflicts within Thai society that Thaksin had created.

Delivering a brief television address in front of giant portraits of Thailand's king and queen, Sondhi said the coup leaders had no intention of retaining power. He was flanked by chiefs of the three armed services and the head of the national police.

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. 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.

The U.S. State Department said it was uneasy about the military takeover and hopes political differences can be resolved through democratic principles. "We are monitoring the situation with concern," a statement said. "We continue to hope that the Thai people will resolve their political differences in accord with democratic principles and the rule of law."