Making the announcement, army chief Gen Prayut Chan-O-Cha, who had declared martial law on Tuesday but denied it was a coup, in a televised statement said that the military takeover was necessary to prevent the conflict from escalating.
"In order for the country to return to normal quickly the National Peace Keeping Committee comprised of the army, the Thai armed forces, the Royal Air Force and the police need to seize power as of May 22 at 4.30 pm (local time)," he said.
Gen Prayut asked all Thais to remain calm and said all government officials must work as normal.
The army sealed off the military facility where the second round of talks between political rivals were being held under the army chief, apparently to block those inside from leaving.
The surprise move came after rival factions failed to reach a compromise to end nearly 7 months of political deadlock and turmoil.
The army chief assumed the role of a crisis mediator on Wednesday in a bid to end the prolonged crisis in the troubled South East Asian nation.
The military -- which has attempted 18 coups, including 11 successful ones, since the end of absolute monarchy in 1932 -- acted after political violence claimed 28 lives and left hundreds wounded.
The military also declared a night-time curfew across the country.
"Under martial law, the National Peace Keeping Committee prohibits anyone across the kingdom from leaving their home from 10 pm to 5 am," an army spokesman said in a televised announcement.
The military ordered all television and radio stations to suspend their usual programmes and show only the army's broadcasts in the wake of the coup.
The move was to ensure the release of "accurate news to the people," the spokesman said.
The army chief said that the military would "provide protection" for foreigners in Thailand. Thailand has been marred by bouts of political violence for more than 7 years.
The latest round of unrest began in November, when anti-government protesters took to the streets to force Prime Minister Yingluck Shinawatra from the office.
They accuse Yingluck of acting as a proxy for her fugitive brother, former premier Thaksin, who was ousted in a coup in 2006.
Earlier this month, a court ordered Yingluck's removal for alleged abuse of power.
She was replaced by caretaker Prime Minister Niwattumrong Boonsongpaisan.
Image: Thai soldiers stand guard as they provide security at the Army Club where Thailand's army chief holds a meeting with groups and organisations with a central role in the crisis, in central Bangkok.
Photograph: Athit Perawongmetha/Reuters
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