SEOUL, South Korea — South Korean President Yoon Suk Yeol declared martial law Tuesday, vowing to eliminate “anti-state” forces as he struggles against an opposition that controls the country’s parliament and that he accuses of sympathizing with communist North Korea.

The surprising move harkened back to an era of authoritarian leaders that the country has not seen since the 1980s, and it was immediately denounced by the opposition and the leader of Yoon’s own conservative party.

Following Yoon’s announcement, South Korea’s military proclaimed that parliament and other political gatherings that could cause “social confusion” would be suspended, according to South Korea’s Yonhap news agency.

The military also said that the country’s striking doctors should return to work within 48 hours, Yonhap said. Thousands of doctors have been striking for months over government plans to expand the number of students at medical schools. The military said anyone who violates the decree could be arrested without a warrant.

It was not immediately clear how long Yoon’s martial law declaration could stand. Under South Korean law, martial law can be lifted with a majority vote in the parliament, where the opposition Democratic Party holds a majority.

National Assembly Speaker Woo Won Shik, in an emergency statement released on his YouTube channel, called for all lawmakers to gather immediately at the National Assembly and urged military and law enforcement personnel to “remain calm and hold their positions.”

TV footage showed police officers blocking the entrance of the National Assembly and helmeted soldiers carrying rifles in front of the National Assembly’s main building to restrict the entrance of people.

An Associated Press photographer saw at least three helicopters, likely from the military, that landed inside the Assembly grounds, while two or three helicopters circled above the site.

Cho Kuk, a leader of a minor opposition party, said there were not enough lawmakers present to vote down the martial law declaration, as police blocked the entrance.

The leader of Yoon’s conservative People Power Party, Han Dong-hoon, called the decision to impose martial law “wrong” and vowed to “stop it with the people.” Opposition leader Lee Jae-myung, who narrowly lost to Yoon in the 2022 presidential election, called Yoon’s announcement “illegal and unconstitutional.”

Yoon said during a televised speech that martial law would help “rebuild and protect” the country from “falling into the depths of national ruin.” He said he would “eradicate pro-North Korean forces and protect the constitutional democratic order.”

“I will eliminate anti-state forces as quickly as possible and normalize the country,” he said, while asking the people to believe in him and tolerate “some inconveniences.”

Yoon — whose approval rating has dipped in recent months — has struggled to push his agenda against an opposition-controlled parliament since taking office in 2022.

Yoon’s party has been locked in an impasse with the liberal opposition over next year’s budget bill. The opposition has also attempted to pass motions to impeach three top prosecutors, including the chief of the Seoul Central District Prosecutors’ Office, in what the conservatives have called a vendetta against their criminal investigations of Lee, who has been seen as the favorite for the next presidential election in 2027 in opinion polls.

Yoon has also dismissed calls for independent investigations into scandals involving his wife and top officials, drawing quick, strong rebukes from his political rivals. The Democratic Party reportedly called an emergency meeting of its lawmakers following Yoon’s announcement.

Yoon’s move is the first declaration of martial law since the country’s democratization in 1987. The country’s last previous martial law was in October 1979.