The US ambassador to South Korea Mark Lippert, has been slashed by a political extremist armed with a razor at a function in Seoul where he was to give a lecture.

Lippert, who became Washington’s envoy in the South Korean capital in October 2014, was taken to hospital with cuts to his hand and face after the attack on Thursday morning. Officials said his injuries were not life-threatening.

His assailant, identified by police as 55-year-old Kim Ki-jong, carried out the attack while Lippert, 42, was attending a breakfast function at the Sejong Cultural Institute in the city centre of the South Korean capital.

Video footage of the immediate aftermath of the attack shows Kim being wrestled to the floor by security guards before being taken away by police. South Korean media reported he had been in possession of a blade 25cm (10 inches) long.

Kim reportedly condemned joint military exercises being held by South Korea and the US, and called for the immediate reunification of the Korean peninsula. Social media pictures showed a blood-spattered tablecloth in front of the chair where Lippert had been seated.

"The guy [Kim] comes in wearing traditional Korean brown and tan dress. He yells something, goes up to the ambassador and slashes him in the face,” Michael Lammbrau, who witnessed the attack, told Reuters.

Lammbrau, who works at the Arirang Institute thinktank in Seoul, added: "People wrestled the guy to the ground, the ambassador was still in his chair. The ambassador fought him from his seat. He was escorted out afterwards. There was a trail of blood behind him. He had about a seven-inch long gash on the right side of his face.”

Lippert looked stunned but was able to walk to his car to be taken to hospital. He was seen holding a handkerchief to a cut on his right cheek; the wrist on his other arm appeared to be bleeding heavily.

Kim continued to yell anti-war slogans after he was subdued, Lammbrau said. "It sounded like he was anti-American, anti-imperialist, that kind of stuff,” he said.

A spokesperson for the US embassy in Seoul said: "We can confirm that there was an incident this morning. The ambassador is in stable condition. We have no further comment at this time.”

In Washington the US state department reacted quickly to the alarming incident on the territory of a staunch regional ally. "We strongly condemn this act of violence,” spokeswoman Marie Harf told reporters.

President Barack Obama spoke with Lippert after the attack, said White House national security spokeswoman Bernadette Meehan.

"The president called US ambassador to the Republic of Korea, Mark Lippert, to tell him that he and his wife Robyn are in his thoughts and prayers, and to wish him the very best for a speedy recovery,” Meehan said.

The South Korean president, Park Geun-hye, said from the United Arab Emirates that the wounding was an "attack on the South Korea-US alliance”.

Kim was already known to South Korean police, having received a two-year suspended prison sentence for throwing a piece of concrete at the Japanese ambassador to Seoul in July 2010, the Yonhap news agency said.

Lippert has proved a popular ambassador during his time in Seoul and is a regular poster on social media. His wife gave birth in the city and the couple gave their son a Korean middle name.

The former US assistant secretary of defence for Asian affairs also served as a foreign policy aide to Obama when Obama was a senator, then during his successful 2008 bid for the White House and on his presidential transition team. The former intelligence officer in naval special operations was awarded a bronze star for his service in Iraq.

South Korea and its communist neighbour to the north have remained effectively at war since 1953, when the three-year Korean war ended in a ceasefire but not a peace agreement. The two countries have remained divided by the demilitarised zone – the world’s most heavily armed border – for more than six decades.

Annual military drills that began last week have been blamed for raising tensions on the peninsula. North Korea routinely condemns the exercises, involving tens of thousands of South Koreans and US troops based in the country, claiming they are used as a practice run for an invasion.

During the drills in 2013 the North Korean leader, Kim Jong-un, threatened nuclear strikes on Washington and Seoul. On Monday the North marked the first day of this year’s exercises by test-firing short-range missiles.

Seoul and Washington insist that the drills, which will end in April, are purely defensive.

Some South Koreans claim the presence of the almost 30,000 US troops as a deterrent in their country is an obstacle to a unified Korea.