SEOUL (REUTERS) - South Korean police said on Friday they have requested a court-issued detention warrant for an assailant who slashed the US ambassador to Seoul in the face, with the charges to include attempted murder.

Ambassador Mark Lippert suffered wounds to his face and hand, and remains in hospital after Thursday's attack, although his injuries are not life-threatening.

Police are investigating possible links between the attack and visits made by the assailant, identified as Kim Ki Jong, to North Korea in the past.

Mr Yoon Myeong Seong, chief of police in the capital's Jongno district, told a news briefing that the suspect visited North Korea seven times between 1999 and 2007.

"We are investigating whether there is any connection between the suspect's visits to North Korea and the crime committed against the U.S. ambassador," Mr Yoon said.

Mr Lippert's case is being handled by a special investigation team comprised of more than 100 prosecutors and police officers, and led by the anti-terrorism bureau of the Seoul Central District Prosecutors' Office.

"There is no evidence yet, but we are trying to find out whether he has violated the national security law," Mr Yoon said.

Enacted in 1948 to protect the fledgling South Korean state from infiltration by the communist North, the law prohibits the spoken or written promotion of North Korean ideology, deeming any such activity to be "anti-state" and subject to up to seven years imprisonment.

Most South Koreans never have visited the secretive North. According to South Korea's Unification Ministry, Kim planted trees near the city of Kaesong, just across the border, during his visits to North Korea.

Kim, who was dressed in traditional Korean clothes, was immediately wrestled to the ground and taken into police custody.

As he was moved from the police station to court on Friday, Kim was asked if he had acted on the orders of North Korea.

"No, nothing like that," he replied, saying the idea was "outrageous".

Prosecutors said they would pursue a charge of attempted murder, given the premeditated nature of the attack.

Kim also faces charges for assaulting a foreign envoy and obstructing business operations. The police raided his home and office early on Friday, looking for evidence of whether he also broke a state security law that bans supporting the regime in Pyongyang.

Kim, who has been identified by police as a member of the pro-unification group that hosted the forum, said the attack was meant as a protest against joint military exercises by South Korean and US troops that began this week.

North Korean state media said the attack against Mr Lippert was"deserved punishment" for the drills, calling the assault "the knife of justice".

South Korea's Unification Ministry condemned the statement, calling it "senseless".

The ministry, which is responsible for inter-Korean affairs, also said it was appalled by the North's response to the assault.

"We strongly censure North Korea for giving support to the incident and distorting its nature," said ministry spokesman Lim Byeong Cheol.

"North Korea should stop its irrational incitement and think seriously about what it should do for the development of inter-Korean relations and true peace on the Korean peninsula," Mr Lim said.

The South Korean government ordered increased security for diplomatic missions, including the US embassy, and the police said on Friday they were providing protection for Mr Lippert.

Mr Lippert was accompanied by a bodyguard when the attack took place on Thursday. The police were also present, although not at the request of the US embassy or organisers.

Doctors at the hospital where Mr Lippert underwent two-and-a-half hours of surgery said the envoy was recovering well.

Mr Lippert underwent surgery on Thursday for an 11cm gash on the right side of his face and a puncture wound on his left wrist that caused nerve damage, which was repaired.

There was no irreversible nerve damage to his face, although a cut to his left hand had damaged the nerves of his little finger that could take six months to repair.

Mr Lippert needed 80 stitches to close a gash in his face. He is recovering in a Seoul hospital and has said he is in "good spirits".

Doctors said on Friday that Mr Lippert was likely to remain in hospital until early next week, when they plan to remove his stitches.