Soldiers swept into the streets of Bangkok, protest leaders were rounded up and international TV networks went dark Thursday after a military coup pitched Thailand into an unsettling new period of political uncertainty.

The coup was bloodless as of Friday morning, but it marked a risky play by the Thai military to take over a polarized country with an already feeble democracy and a beloved but ailing king.

In launching the coup, the Thai military swiftly detained or marginalized the key players in months of turmoil. The military has ordered recently deposed prime minister Yingluck Shinawatra, as well as dozens of her powerful relatives, to appear at an army facility Friday morning.

U.S. officials quickly condemned the takeover and warned that they were reviewing military and other assistance to Thailand. The coup could inflame tensions by eliminating an elected government and sidelining a boisterous opposition group.

Months of tensions have already battered Thailand’s tourism-based economy, but the coup quickly darkened one of Southeast Asia’s most vibrant capitals. The army announced a nationwide curfew from 10 p.m. until 5 a.m., in effect until further notice. Commuters scrambled to get home Thursday, and soon after dinner, only a few confused tourists were still out on the streets.

In a televised announcement, Gen. Prayuth Chan-ocha, commander in chief of the Royal Thai Army, said the coup would help a fractious country “return to normal quickly” after months of political instability. “The military has to return peace and order to the country as soon as possible,” Prayuth said.

[Read: Here are the last 11 coups staged by Thailand’s military.]

Soon after the coup, the military said it had suspended the constitution, dismissed the caretaker government and ordered cabinet ministers to turn themselves in. Prayuth was proclaimed the head of a council that will temporarily run the country.

Meanwhile, soldiers went to various pro- and anti-government sites across the capital, Bangkok, detaining some of the leaders deemed responsible for Thailand’s protracted political crisis.

Although the extent of military control of the country was not immediately evident, initial reports indicated that troops were able to clear protest sites in a fairly orderly manner.

In Washington, Secretary of State John F. Kerry said that “there is no justification for this military coup” and warned that there would be “negative implications for the U.S.-Thai relationship, especially for our relationship with the Thai military.”

In a statement, Kerry said he was concerned by reports that senior political leaders had been detained and that news media outlets had been shut down. “I urge the restoration of civilian government immediately, a return to democracy, and respect for human rights and fundamental freedoms, such as press freedoms,” he said.

State Department spokeswoman Jen Psaki said $10 million in annual U.S. aid to Thailand was under review.

Thailand is notorious for its political instability and periodic military takeovers. Since the establishment of a constitutional monarchy in 1932, there have been 12 successful coups and seven attempted ones. But Thailand now finds itself at a particularly dangerous moment, and some analysts warn that its intensifying divisions could lead to armed clashes or, in the worst case, civil war.

Seized at peace talks

The Thai military launched its coup Thursday under the guise of peace talks, which it was brokering. For the second day in a row, representatives from both sides of the country’s main political divide showed up at a military site in the afternoon. This time, according to local media reports, at least some were not allowed to leave, and other protest leaders were soon rounded up across Bangkok.

Among those detained was Suthep Thaugsuban, the leader of the anti-government movement. The pro-government group, known as the “red shirts,” said on Twitter that some of its leaders were also detained.

The coup comes two days after the military declared martial law, pledging that it would not remove the government. In imposing martial law, the military cited a century-old law that gave it broad powers to censor the media, detain civilians and outlaw meetings or assemblies.

For the past half-year, Thailand has been nearly paralyzed by a conflict that has left about
30 people dead and hundreds injured. The conflict, at its core, is a power struggle between rural voters in the vast northern part of the country and urban elites in Bangkok. The rural voters outnumber the urban ones, and over the past 13 years, they have found a political party they love. Again and again they vote it into office, even as the party cycles through leaders. And again and again, those leaders are ousted by court rulings or coups.

The conflict is testy, because both sides have major grievances. Those who oppose the ruling party, now known as the Pheu Thai, say it is ruled by a de facto strongman, Thaksin Shinawatra, who has let corruption run rampant and consolidated power in his family and cronies.

Thaksin’s supporters say the country has found dubious ways to oust a democratically elected party. He was removed as prime minister by a military coup in 2006 and now lives in Dubai.

His sister, Yingluck Shinawatra, became prime minister in 2011 when Pheu Thai won general elections. But she was booted from office two weeks ago after Thailand’s Constitutional Court found her guilty of abuse of power.

Coups in Thailand are often bloodless, but this is the first to come at a time when the country’s beloved king, Bhumibol Adulyadej, 86, appears too ill to play his traditional mediator role.

Opposition to Yingluck mounted late last year when the parliament attempted to pass legislation that would have given amnesty to Thaksin and others facing political charges.

After the implementation of martial law Tuesday, the military set up what it described as a “Peace and Order Maintaining Command.” A day later, the military summoned representatives from the caretaker government as well as the two major rival political factions for supposed peace talks.

On Thursday, the attendees were taken into custody. Video from the scene shows Suthep, the anti-government protest leader, being hustled into a white van and driven away.Thailand’s caretaker prime minister — Niwattumrong Boonsongpaisan, who replaced Yingluck — did not attend the meetings. Niwattumrong was not detained in any of the subsequent roundups, but some news media reports said he had been ordered to turn himself in.

Early Friday, Bangkok was business as usual, as Thais drove, biked, taxied and took public transportation to work. The only hints that something was awry were the comparatively minor traffic jams and the fact that schools and educational institutions are closed through Sunday.

Locals and foreigners alike were out and about, many seemingly oblivious to the coup.

Three 20-something Americans, Texans who teach English in Thailand, strolled around the central business district Two had arrived the day the coup was launched.

“If you didn’t have the news on you’d never know there was a coup,” said Michael, who has been in Thailand one year and did not want to reveal his last name.

Samuels reported from Bangkok. Karen DeYoung in Washington contributed to this report.