South Korean police on Wednesday searched the office of President Yoon Suk Yeol, as part of a widening investigation into his failed imposition of martial law last week.

Police investigators presented a search warrant that specified the president as the suspect, the Yonhap news agency reported, in a dramatic escalation of the probe against Yoon.

"The Special Investigation Team has conducted a raid on the presidential office, the National Police Agency, the Seoul Metropolitan Police Agency, and the National Assembly Security Service," the unit stated in a message sent to the French AFP news agency.

Meanwhile, former South Korean Defence Minister Kim Yong-hyun, who is believed to have played a key role in the failed imposition of martial law, attempted to take his own life while in custody.

The attempt failed and Kim is still alive. 

What we know about the suicide attempt

The former defense minister was formally arrested on charges of "engaging in critical duties during an insurrection" and "abuse of authority to obstruct the exercise of rights."

Kim attempted suicide shortly before midnight (1500 GMT Tuesday), said the commissioner general of the Korea Correctional Service Shin Yong-hae. 

He had tried to kill himself using a string from his clothing, he added.

"A control room staff member intervened, and when they opened the door, he immediately gave up the attempt," said Shin. 

Kim is now under protection and in good health.

Second impeachment attempt scheduled

South Korea's main opposition Democratic Party is set to submit a second motion to impeach Yoon. Their first attempt failed last Saturday when the ruling party blocked the vote.

A few of Yoon's top officials have already been arrested, detained and questioned about their role in imposing martial law on the country.

The imposition of martial law has deeply impacted South Korean politics and foreign policy, as well as its financial markets.

Experts and the opposition say the imposition of martial law is warranted only during national emergencies, wartime or war-like situations by law.

The leader of the conservative ruling party has promised Yoon's exit from power and an early election. But the plans have been criticized for being unconstitutional.

tg/rmt (AFP, AP, Reuters)