U.S. Ambassador to South Korea Mark Lippert expressed his "profound gratitude" on Tuesday for the overwhelming support he received from South Koreans and Americans alike after he was knifed by a South Korean nationalist last week.

"I feel pretty darn good all things considered," Lippert told reporters before he left the hospital. "I want to express my profound gratitude to those Koreans and Americans alike who so bravely, gratefully and selflessly responded to the scene of the attack and the medical team that delivered a world-class treatment."

The envoy also stressed that relations between South Korea and the U.S. will remain as strong as ever, as officials from both countries have already agreed.

"This incident has only strengthened our love and affection for this country and our belief in the unbreakable bond that exists between the United States and the Republic of Korea," he said.

"I will still be a 'dongne ajeossi' and 'sejuni appa,' as people in Korea have called me," he added, referring to his Korean nicknames, roughly translated as "a dude in the neighborhood" and "Sejun's dad." Sejun is the Korean middle name Lippert gave to his son, who was born here in January.

Lippert spent five days at Yonsei University's Severance Hospital. Hospital officials said he will continue to receive treatment from home.

Jung Nam-shik, head of the Yonsei University Health System, said the wounds on Lippert's left arm will require regular sterilization to prevent infection. The ambassador continued to experience pain in his left wrist, but it was manageable with a mild painkiller, Jung added.

Lippert was slashed on his face and wrist last week by a knife-wielding South Korean man who attacked him at a breakfast function in downtown Seoul.

Kim Ki-jong was arrested at the scene and has been detained on various charges, including attempted murder.

Kim said he assaulted the ambassador to alert the U.S. to "the fact that it hinders inter-Korean reunification." He denies having meant to murder the envoy.

South Korea remains technically at war with rival North Korea, with the U.S. stationing more than 28,000 troops here to deter North Korean aggression. Hard-core nationalists here argue that the U.S. gets in the way of Korean reunification, as Pyongyang considers U.S. troops here threatening.

Kim was convicted in 2010 of throwing pieces of rock at a Japanese ambassador to Seoul. It was the first incident in South Korea in which a foreign envoy was attacked by a local.

He fractured his right ankle when authorities overpowered him on Friday and will undergo surgery at the National Police Hospital this afternoon. Police said the interrogation will continue at the hospital.

Authorities are continuing their probe to determine whether Kim has violated a controversial security law that bans people from openly praising North Korea.

Kim was already found to have traveled to the North seven times between 1999 and 2007. He also tried to erect an altar in the heart of Seoul that honors late North Korean leader Kim Jong-il in 2011, according to authorities.

About a dozen books were recently found in Kim's home that are suspected of being dangerously pro-North Korea in nature, including "On the Art of Cinema" written by Kim Jong-il.

Possession of pro-North Korea books alone would not be sufficient to charge Kim with violating the National Security Law.

Authorities would need to prove that Kim tried to threaten national security or destabilize South Korea's democratic order with these materials.

Kim reportedly told officers he considers North Korean founder Kim Il-sung a "great leader of the 20th century" with no leader in South Korea coming close.

Lippert, 42, is the youngest U.S. ambassador to South Korea. He took office in October and his wife gave birth to a son here. His son was given a Korean middle name.

Meanwhile, police have apprehended a 71-year-old man who allegedly called in a phone treat to YTN, a local cable news channel, earlier Thursday to protest the TV showing of Lippert's injured face.

The man, identified only by his surname Song, allegedly called to say he would blow up the YTN headquarters if the channel continued to show Lippert's injured face on TV.

Song reportedly said he had made several such requests before and would not tolerate another display of Lippert's injury.

He was arrested near Seoul's YTN headquarters about six hours after the call was made. Police are investigating his motive. (Yonhap)