South Korea US envoy Lippert 'well' after knife attack
Mark Lippert, 42, was also cut on his left hand, with blood spattered over the breakfast table.
Security officers subdued the attacker, one pinning him down with a shoe on his neck, until he was arrested.
Mr Lippert had hospital treatment but later said he was "doing well".
"Doing well and in great spirits!" he wrote in a tweet. "Will be back ASAP to advance US-ROK [Republic of Korea] alliance!"
US President Barack Obama called his ambassador to wish him "the very best for a speedy recovery", a US official said.
The US state department said it strongly condemned the incident which South Korean President Park Guen-hye described as an "attack on the South Korea-US alliance".
Witnesses say the attacker, a 55-year-old man with a history of militant Korean nationalistic activism, shouted demands for North and South Korea to be reunified.