Kim Ki-jong, a member of a pro-Korean unification group who attacked the US ambassador to the Republic of Korea Mark Lippert at a public forum, is carried on a stretcher off an ambulance as he arrives at a hospital in Seoul March 5, 2015. [Photo/Agencies]

SEOUL -- Republic of Korea (ROK)'s prosecutors on Tuesday sought a 17-year prison term against a 56-year-old attacker of Mark Lippert, US ambassador to the ROK, at an appeals court.

The prosecution sought the longer jail term during a hearing at the Seoul High Court as the ROK man slashed the face and arm of the top US envoy to Seoul with a knife that needed more than 80 stitches.

Kim Ki-jong, who is serving an imprisonment, was sentenced to 12 years in prison at the lower court for attacking Lippert at a breakfast function in Seoul in March last year.

Later, one and a half years of jail term was added as he assaulted a prison guard and a doctor.

Prosecutors asked the appeals court to convict him for the violation of the national security law, which the lower court acquitted him of.

The prosecution reportedly said that Kim committed the crime in sympathy with the Democratic People's Republic of Korea's ideology, noting that his crime was premeditated given a fact that he prepared a knife in advance.