U.S. Ambassador Mark Lippert left a South Korean hospital Tuesday after five days of treatment because of a knife attack by a man screaming about Korean unification, vowing not to change his "open and friendly" approach to diplomacy.

Lippert told reporters assembled at Seoul's Severance Hospital that he felt "pretty darn good, all things considered" after the "scary incident" on Thursday, when police say an anti-U.S. activist slashed his face and left arm during a breakfast forum in Seoul.

Lippert, his face bandaged and his arm in a brace, would not comment on the specifics of the attack because of the police investigation. He refused to discuss possible new security measures, except to say U.S. officials would take "a hard look" at procedures in South Korea and then make a decision.

Lippert, who has endeared himself to many South Koreans by regularly walking his basset hound around his compound in downtown Seoul and giving his newborn son a Korean middle name, said he was deeply moved by messages of support. He said the attack would only strengthen an "unbreakable bond" between Seoul and Washington as the allies work to deepen military, economic and cultural ties.

Media images of the bleeding ambassador shocked many in South Korea, a strong U.S. ally since the Korean Peninsula was split into a pro-American south and pro-Soviet North at the end of World War II, and caused an outpouring of public sympathy. President Park Geun-hye visited Lippert while activists held a series of pro-U.S. rallies near the U.S. Embassy in Seoul.

Doctors removed the 80 stitches needed to close the cut on Lippert's face, Severance's general director Yoon Do-heum told reporters. He said the ambassador still feels some pain in his arm, but it is manageable with medicine. He may experience sensory problems in his left hand for several months.

The alleged attacker, known as an anti-U.S. activist who was previously convicted of hurling a piece of concrete at the Japanese ambassador in Seoul in 2010, was arrested Friday. Kim Ki-jong could face charges including attempted murder.

Police said the motive for Kim's action was not known, but he shouted after the attack that he opposes the ongoing annual U.S.-South Korea military drills that North Korea condemns as a preparation for a northward invasion. Seoul and Washington call the drills defensive and routine.

Critics have raised fears that President Park's conservative government might use the attack to crack down on those seen as pro-North Korea. Already they say Park's government infringes on freedom of speech in the name of coping with North Korea sympathizers.

Last year, a Korean-American woman accused of praising North Korea was deported, and the Constitutional Court ordered the dissolution of a small leftist party that officials say advocated a North Korean-style socialist system.

The two Koreas are divided along the world's most heavily fortified border, and the Korean Peninsula is still technically at war since the 1950-53 Korean War ended with an armistice, not a peace treaty. The U.S., which fought alongside South Korea during the war, stations about 28,500 troops in the South as a deterrent against the North.