South Korean police on Wednesday raided the residence and office of a man who stabbed the country's Opposition leader, Lee Jae-myung, in the neck in an attack that left him hospitalized in an intensive care unit, officials said.

The assault occurred when Lee was passing through a throng of journalists after visiting the proposed site of a new airport in the southeastern city of Busan on Tuesday. The attacker, posing as a supporter, approached Lee asking for his autograph before he took out a 18-centimeter (7-inch) knife to attack him.

After receiving emergency treatment in Busan, Lee was transported by a helicopter to the Seoul National University Hospital for surgery. Cho Jeong-sik, the party's secretary general, said Wednesday the two-hour surgery was successful and that Lee remained in the hospital's intensive care unit for recovery. Police and emergency officials earlier said Lee was conscious after the attack and wasn't in critical condition.

The suspect was detained by police immediately after the attack. Police said he told investigators he attempted to kill Lee and that he had plotted his attack alone, but his motive is unknown.

Busan police said they sent officers to search the suspect's residence and office in the central city of Asan on Wednesday as part of their investigation. Police said they plan to ask for a formal arrest warrant for the suspect over alleged attempted murder.

Police disclosed few further details about the suspect except that he was aged about 67 and bought the climbing knife online. Police refused to disclose what kind of office he has in Asan, but local media photos showed officers searching a real estate office.

Lee, 59, is a tough-speaking liberal who lost the 2022 presidential election to President Yoon Suk Yeol by 0.7 percentage points, the narrowest margin recorded in a South Korean presidential election. Their closely fought presidential race and post-election bickering between their allies have deepened South Korea's already-toxic conservative-liberal divide.

Recent public surveys have put Lee as one of the two leading early favorites for the next presidential election in 2027, along with Yoon's popular former justice minister, Han Dong-hoon. Yoon is by law barred from seeking reelection.

In a New Year meeting involving top officials, politicians and general citizens on Wednesday, Yoon repeated his wish for Lee's quick recovery. He also condemned the assault on Lee as “a terrorist attack” that is “an enemy to all of us and an enemy to liberal democracy,” according to his office. Lee was supposed to attend that meeting.

Lee has been a vocal critic of Yoon. Last year, he launched a 24-day hunger strike to protest Yoon's major policies, including what he called Yoon's refusal to firmly oppose Japan's release of treated radioactive wastewater from its crippled Fukushima nuclear power.

Lee has been grappling with a prolonged prosecutors' investigation over a range of corruption allegations. Lee has denied legal wrongdoing and accused Yoon's government of pursuing a political vendetta.