South Korean police say they are seeking charges of attempted murder against a man who slashed the US ambassador to Seoul.
Ambassador Mark Lippert is recovering in hospital after Kim Ki-jong attacked him with a knife on Thursday.
During the attack, Mr Kim called for reunification of the two Koreas.
Police said they were also investigating Mr Kim's links with North Korea, after it was revealed he had made multiple visits.
"We are investigating whether there is any connection between the suspect's visits to North Korea and the crime committed against the US ambassador," Yoon Myeong-seong, head of Seoul's central Jongno district said according to Reuters.
Mr Kim also had a history of nationalist militant activity, media reports said.
A small group of people in South Korea see the US as the main obstacle to the reunification of a divided Korean peninsula.
Mr Yoon said authorities wanted to charge Mr Kim, 55, with attempted murder, violence against a foreign envoy and business obstruction, Yonhap news agency reported. Police have requested a formal detention warrant.
Mr Kim, who was apprehended after the incident, told police that he did not intend to kill Mr Lippert.
Mr Yoon also said they were considering charging him with violating South Korea's National Security Law, which bans South Koreans from publicly sympathising with the government of North Korea.
Mr Kim also shouted opposition to annual US-South Korean military drills, which began Monday, during the attack.
North Korea traditionally opposes the drills, which it describes as a rehearsal for invasion. Late on Thursday, it described the attack as "just punishment for US warmongers", in a statement on state media.
Mr Lippert, 42, was given 80 stitches to the deep cut on his face and underwent surgery to repair nerve damage to his hand.
Doctors said he would be discharged early next week.
The attack raised questions about security for diplomatic personnel. Mr Lippert had a bodyguard with him when the attack took place. Police were also there, but not at the request of the US embassy or the organisers of the event.
The responsibility for the safety of diplomats lies with the host nation.
After the incident, the South Korean government ramped up security for diplomatic missions, including the US embassy. Police said they were providing protection for Mr Lippert.
Kim Ki-jong's militant past
- In 1985, was part of a group that cut and burned a US flag on the embassy grounds in Seoul, according to South Korea's Yonhap news agency
- Visited North Korea at least six times in 2006-07, reportedly planting trees near the border city of Kaesong
- In 2007, set himself on fire in front of the presidential office in Seoul, asking for an inquiry into a rape that had allegedly taken place at his office in 1988 (Yonhap)
- When in 2010 he hurled concrete at the then Japanese envoy, Toshinori Shigeie, it was the first assault on a foreign ambassador in South Korea; he received a suspended jail term
- In 2011, he tried to erect a memorial altar for the late North Korean leader, Kim Jong-il, in the heart of Seoul (Yonhap)
- Has also staged one-man protests against Japan over an island dispute (Reuters)