North Korean state media has welcomed the knife attack on the American ambassador to South Korea Mark Lippert calling it a "punishment" as the US Embassy in Seoul beefed up security.

Lippert was taken to a hospital where he a three-hour surgery after suffering wounds to his face and arm. Hospital officials said that Lippert suffered a four-inch-long gash down the right side of his face, which required 80 stitches.

The diplomat said he was "doing well and in great spirits" following the attack, writing in a Twitter post that he "will be back ASAP."

A hospital official told reporters that "some paralysis of his face and left arm senses are expected."

Police said that the attacker shouted that the rival Koreas should be unified as targeted the envoy. Police are considering whether to charge 55-year-old Kim Ki-jong with attempted homicide.

The attack is seen as a protest against joint military exercises by South Korean and U.S. troops, which according to Kim interfered with reconciliation between North and South Korea, police said after quizzing the suspect.

"I carried out an act of terror," Kim shouted as he was pinned to the floor by people at the event.

North Korea's official KCNA news agency called the attack "deserved punishment" and "the knife of justice" for U.S. military exercises with South Korea.

Police said that a small fruit knife was used by the attacker. The envoy was attacked in a government arts center across the street from the heavily guarded U.S. Embassy on the South Korean capital's main ceremonial thoroughfare. South Korean police has increased the security to the U.S. Embassy following the attack.