South Korea expressed deep shock and regret over the knife attack on U.S. Amb. to South Korea Mark Lippert on Thursday, vowing to step up safety protection for foreign envoys and embassy facilities here.

A progressive 55-year-old activist cut Lippert's face and wrist with a 25-centimeter knife as the ambassador was preparing to give a lecture at a breakfast function in central Seoul.

The assailant shouting anti-war slogans was immediately arrested while Lippert, bleeding, was rushed to a nearby hospital.

The U.S. State Department said his injuries are not life-threatening and strongly denounced the violence.

"The government cannot repress its shock over the violence inflicted on Ambassador Lippert and is feeling very regretful," Noh Kwang-il, spokesman for the Ministry of Foreign Affairs, said in a statement.

Acts of violence against foreign envoys are never pardonable and the government is taking the attack on the ambassador from the U.S. -- one of its most important allies -- seriously, the spokesman said.

The government plans to thoroughly investigate the attack and take stern action, Noh said, adding that "it will make all efforts for the safety and protection of foreign envoys and embassy facilities."

The spokesman also extended its consolation to the family of the injured ambassador, expressing hopes for Lippert's prompt recovery.

Seoul's foreign ministry said Seoul and Washington have agreed to cooperate in a bid to prevent the incident from having a negative impact on the allies' relationship.

"The two countries have decided to closely cooperate to prevent this incident from negatively affecting the Seoul-Washington alliance," a ranking official at Seoul's foreign ministry told reporters.

The official said that the two sides agreed that it is important to curb the spread of misunderstanding and negative sentiment in both countries.

Experts said the unprecedented attack on the U.S. ambassador would not bring about an immediate setback in relations with the U.S. although South Korea is feared to suffer a tainted national image inside the U.S.

"If it was an impulsive act conducted on a personal level, not in an organized manner, the repercussion (from the incident) will not be so serious," said Yun Duk-min, head of the Korea National Diplomatic Academy.

"Nevertheless, it could impair (U.S.) impressions and image vis-a-vis South Korea as the assailant took issue with wars in context of joint Seoul-Washington military exercises. It could also taint the image (of South Korea) as a safe nation," he noted.

Choi Kang, vice chief of the Asan Institute for Policy Studies, said, "At the government level, not only South Korea but the U.S. also may try to resolve the issue as soon as possible by diminishing the attack as an impulsive personal act."

But it may further complicate South Korea-U.S. ties with the allies somewhat at odds over the recent controversial remarks by Undersecretary of State Wendy Sherman, Choi noted.

Sherman came under fire here for her remarks in a seminar in Washington last week, which appeared to take side with Japan over the sensitive history of Japan's wartime misdeeds. (Yonhap)