People hold placards showing US Ambassador to South Korea Mark Lippert during a rally denouncing the attack on the US ambassador in Seoul on Tuesday. Photo: AFP

The US Ambassador to South Korea said on Tuesday he plans to maintain his open, approachable style despite being slashed by a knife-wielding Korean nationalist five days ago, causing him wounds that required 80 stitches in his face.

Mark Lippert quickly became known for his informal demeanor after becoming ambassador in November but last week's attack raised questions about his security arrangements.

"We have made it our mission to be open and friendly and that will not change," Lippert, 42, told a media conference amid heavy security after he was released from hospital. He declined to comment about potential changes to his security arrangements.

Police are seeking to bring charges including attempted murder against Kim Ki-jong, 55, for the attack at a forum discussing Korean reunification.

Kim was given a suspended jail sentence in 2010 for throwing a piece of concrete at the Japanese ambassador. He said after he attacked Lippert he was protesting against annual US-South Korean military drills, which began last week.

"We are going to have a hard look at our tactics, technique, procedures here. I will leave it to the security experts to come up with recommendations and policies going forward," Lippert said.

The United States is South Korea's closest ally and maintains a military presence of 28,500 personnel. While that has drawn protest from some South Koreans in the past, opposition has eased in recent years.

Lippert was accompanied by his bodyguard when the attack took place at a theatre across the street from the heavily guarded US embassy. Other police officers were present, although not at the request of the embassy or organizers.

Until the attack, Lippert was the only head of a diplomatic mission in Seoul assigned such protection, according to the US State Department. Since then, Seoul has ordered increased security for diplomatic missions, including the US embassy.

Lippert could often be seen around Seoul walking his dog, and tweets regularly. His blog has regular bilingual posts about his activities and urges people to stop him on the street.

Lippert suffered a puncture wound on his wrist as well as the facial gash but said he was feeling well. "By and large, I felt very, very safe in Seoul."