SEOUL (AFP) - North Korea hit out Sunday at accusations that it may be behind a shocking knife attack on the United States envoy to the South, branding the claims a "vicious" smear campaign by Seoul.

Kim Ki Jong slashed Mr Mark Lippert with a paring knife on Thursday, in an assault that left the US envoy needing 80 stitches to a deep gash on his face.

On Sunday the North's Committee for the Peaceful Reunification of Korea (CPRK) bristled at suggestions that it might have been behind the assault, calling it an attempt to defame its leadership. "Even the police and conservative media of South Korea joined the (South's) regime in attempting to link the case with the (North)," it said in a statement carried by the state-run KCNA late on Saturday.

"Such moves are prompted by a vicious intention to save itself from the present awkward position... and intensify an anti-DPRK smear campaign worldwide," the CPRK said, using the North's official title.

Kim, 55, was immediately arrested and charged with attempted murder, and the police are investigating whether he has any links to the communist North. He has reportedly told the police that he had acted alone and denied any links to the North, calling the suggestion "outrageous".

After the attack on Thursday, the North hailed Kim's act as "just punishment" and a valid "expression of resistance" to the US-South military drills.

Last week the police raided Kim's house in search for evidence of his potential links to the North.

Police are investigating whether Kim violated the South's notorious, anti-communist national security laws, which ban unauthorised contact with the North or activities deemed to be praising Pyongyang.

The profile painted of Kim - based on past brushes with the law and his blog postings - is that of a lone assailant with strong nationalist views who saw the US as one of the main obstacles to the reunification of the divided Korean peninsula.

But Kim also visited the North seven times since 1999 and once tried to erect a memorial in Seoul to the late North Korean leader Kim Jong Il after his death in 2011.

Kim told the police he had stabbed Mr Lippert in protest at massive US-South joint army exercises currently underway. The annual exercises are routinely slammed by the North as a practice for invasion.

Mr Lippert, 42, is recovering well and expected to be released from the hospital as early as Tuesday, his doctors say.