South Korean President Park Geun-hye said on Thursday a knife attack on the U.S. ambassador to Seoul was an "attack on the South Korea-U.S. alliance," Park's office quoted her as saying from the United Arab Emirates.

Ambassador Mark Lippert was slashed in the face by a member of a pro-Korean unification group at a public forum held in the South Korean capital. His injuries were not life-threatening and he is in stable condition in hospital, officials said.