U.S. Ambassador to Korea Mark Lippert was attacked by a knife-wielding leftist activist in downtown Seoul Thursday during a morning seminar, leaving the top U.S. envoy with a 11-centimeter wound and a significant task for Seoul to mend an unprecedented dent in the alliance with Washington.

Lippert was attacked by the 55-year-old suspect, Kim Ki-jong, who reportedly ran toward the ambassador, at around 7:40 a.m., with a 25-centimeter-long paring knife. The ambassador had begun to eat breakfast before a speech during the forum organized by the Korean Council for Reconciliation and Cooperation.

The bleeding diplomat was rushed to a nearby hospital for emergency treatment and then to another where he received surgery for the cut stretching from his right cheek to his chin and another injury on his left arm. He is in stable condition, medical officials said.

Kim was held down by the forum participants right after the attack and arrested. The suspect claimed his attack was aimed at “stopping a war on the Korean peninsula” citing his opposition to the ongoing joint drill by the U.S. and South Korean militaries that is strongly opposed by North Korea.

The incident came after the public sentiment against the U.S. deteriorated following U.S. Under Secretary of State for Political Affairs Wendy Sherman’s recent remarks that suggested Seoul and Beijing were to blame for frayed relations with Japan over history issues.

It was the first time a U.S. ambassador to South Korea has been attacked. The incident occurred just about four months after Lippert, a close confidant of President Barack Obama, assumed office at age 41 -- the youngest-ever American ambassador to Seoul.

Mindful of possible negative ramifications on its alliance with the U.S., Seoul expressed “shock and deep regrets” over the attack and decided to “sternly” punish its officials in charge of protecting the U.S. diplomat.

Police vowed to thoroughly investigate the case and beefed up its security of the U.S. Embassy staff and buildings.

Seoul and Washington agreed to closely cooperate to prevent the attack from negatively influencing their alliance, Seoul officials said.

During the breakfast conference, Kim was sitting at a table right next to the head table where Lippert was preparing for a speech. Witnesses said the attacker abruptly approached the diplomat, pushed him onto the table and slashed him.

Lippert’s surgery lasted for some two and a half hours, and medical officials said that it was “successful.”

“The cut on his face was 11-centimeter-long and 3-centimeter-deep, and the cut on his arm was about 2-centimeter-long and 2-centimeter-deep. He received some 80 stitches on his face,” said Chung Nam-sik, head of the Yonsei University Health System at a news conference.

“He will need hospitalization for some three to four days. And we will need to watch him carefully, but our concerns for now are about the scars on his face and any aftereffect from the cuts on his wrist,” he added. Other medical officials said that the scars would almost disappear one or two years later.

Right after his arrest, Kim, the head of the leftist group, “Urimadang,” shouted, “I carried out the terror attack. I have prepared to disseminate leaflets to oppose the (South Korea-U.S.) military exercise for a war.”

In the leaflet, he called for the “suspension of the exercise that blocks inter-Korean dialogue and Seoul’s retaking of wartime operational control (from Washington).”

Kim claimed his right ankle broke when the police restrained him He was carried away on a stretcher, and told reporters, “I oppose the military drills, a reason why the two Koreas can’t hold the reunions of separated families.”

He also said that he prepared for the attack for some 10 days, and that there was no accomplice or any directives to carry out the attack. “I made a sacrifice myself so as to stop the Key Resolve exercise,” he said.

Officials of the forum’s organizer said that Kim was not invited to the event, but they could not block him from entering because he expressed his wish to attend, and the organizers had no authority to block his entry.

It was not his first attack on foreign diplomats. In 2010, he hurled blocks of concrete toward then-Japanese Ambassador Toshinori Shigeie during his lecture in Seoul. He was given a two-year jail term suspended for three years.

According to intelligence officials, Kim shifted focus from anti-Japan activities to anti-U.S. campaigns after he visited North Korea multiple times. Seoul’s Unification Ministry said that Kim, who served as a member of the state unification education panel, visited the North Korean border city of Gaeseong eight times between 2006 and 2007 on a mission to plant trees.

Investigators appear to believe it was his personal decision to carry out the attack. Police plan to raid and search Kim’s house and seek an arrest warrant to detain him for a longer period on charges of attempted murder and possession of a lethal weapon.

By Song Sang-ho (sshluck@heraldcorp.com)