The motive behind the attack on the US ambassador to South Korea is unknown, according to the State Department in Washington.
The US Secretary of State John Kerry, speaking in Saudi Arabia, vowed that his country would never cede to threats.
Mark Lippert says he’s recovering well after surgery to treat wounds to his face and arm following the knife assault at a breakfast forum in Seoul.
He needed 80 stitches to close the gash in his face.
The 42-year-old was also treated for a puncture wound on his wrist and is expected to remain in hospital for three to four days.
South Korean police showed off the knife – about 25 centimetres long – said to have been used to attack the ambassador as he shook hands.
The man identified as 55-year-old Kim Ki-jong is a member of the pro-unification group that hosted the event, and had previously been arrested in 2010 for trying to attack a Japanese official.
As he was constrained and taken away following the knife attack he shouted that he was against “war exercises”.
Citing joint military exercises between South Korea and the US, North Korea praised the attack as a “deserved punishment”.
That prompted an angry protest in Seoul from about 100 South Korean conservatives who denounced the assault.
Doing well&in great spirits! Robyn, Sejun, Grigsby & I – deeply moved by the support! Will be back ASAP to advance US-ROK alliance! 같이 갑시다!— Mark Lippert (@mwlippert) March 5, 2015
Meanwhile as the US vowed never to cede to threats, the ambassador himself said he was well and in great spirits in a tweet referring to his wife, newborn son and dog.
Mark Lippert became ambassador to South Korea last year.