US ambassador to South Korea Mark Lippert waves as he leaves a hospital in Seoul March 10, 2015. [Photo/Agencies]

SEOUL - A knife attacker of Mark Lippert, US ambassador to South Korea, was sentenced to 12 years in prison for attempted murder.

The Seoul Central District Court on Friday sentenced Kim Ki-jong, head of a South Korean cultural activity group, to the 12- year imprisonment for his attempt to kill the US envoy to Seoul.

Lippert, who took office last year as the youngest envoy for the post, was slashed in March in his cheek and hand with a knife blade when he was preparing for a lecture at a function in Sejong Cultural Center in central Seoul.

The US ambassador was hospitalized for five days as he received 80 stitches in treatment on his cut in right face and left hand.

The assailant shouted his strong opposition to "war exercises" while he was being arrested, indicating the annual war games between Seoul and Washington code-named Key Resolve and Foal Eagle.

Kim already received a suspended two-year jail term for throwing stones at the Japanese ambassador to South Korea in July 2010.

The court acquitted Kim of the violation of national security law, saying his violent acts could not be seen as doing damage to the existence of the country though the acts can worsen the South Korea-US relations.

Prosecutors plan to appeal to the higher court for the lower prison term and the violation of the national security law.