Thailand’s army chief announced a military takeover of the government Thursday, saying the coup was necessary to restore stability after six months of political deadlock and turmoil.

Gen. Prayuth Chan-ocha said in a statement broadcast on national television that the same military commission that had imposed martial law Tuesday would now take control of the country’s administration. Prayuth will head the body, a deputy spokesman said late Thursday.

The army also announced a nationwide curfew from 10 p.m. to 5 a.m. and a suspension of the country’s constitution.

“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 p.m.,” Prayuth said.

U.N. Secretary General Ban Ki-moon said Thursday that he was “seriously concerned” about the developments, and appealed for the military to return Thailand to civilian rule.

U.S. Secretary of State John Kerry said there was “no justification” for the military coup, according to a State Department news release. “While we value our long friendship with the Thai people,” Kerry said in the release, “this act will have negative implications for the U.S.-Thai relationship, especially our relationship with the Thai military. We are reviewing our military and other assistance and engagements, consistent with U.S. law.”

The army has banned gatherings of more than five protesters, and told anti-government protesters to leave the square in Bangkok where demonstrations have been taking place since November.

More: Thailand Army Carries Out Coup, Takes Control of Government