'Threat' Will Never Deter US, John Kerry Says After Korea Slashing

Threats will never deter the United States, Secretary of State John Kerry said on Thursday after an activist slashed the US ambassador to South Korea in the face.

"The United States of America will never be intimidated or deterred by threat or by anybody who harms any American diplomat," Kerry told reporters during a visit to Saudi Arabia.

"We will remain as resolved as ever to pursue what we believe is in the interests of our country and with respect to universal rights and values."

Ambassador Mark Lippert was in stable condition after receiving 80 stitches to a deep gash on his right cheek after the attack by an activist seeking reunification of the Korean peninsula.

Kerry, who called the ambassador to offer personal wishes for his recovery, said Lippert is "as tough as they come".

Witnesses described how a man armed with a 25-centimetre (10-inch) paring knife lunged across a table and attacked the ambassador at a breakfast function in central Seoul.

The assailant, dressed in traditional Korean clothes and identified as Kim Ki-Jong, 55, was immediately wrestled to the ground and taken into police custody.

During the assault, Kim screamed a slogan in favour of reunifying the divided Korean peninsula, and later shouted his opposition to ongoing joint US-South Korean military exercises.