The most controversial moustache in South Korea has fallen victim to the razor's blade, with US ambassador Harry Harris visiting a traditional barbershop months after his facial hair became the object of unusual criticism.

Seoul and Washington are security allies and the US stations 28,500 troops in the country. But their relationship has been strained in recent years by differences in their approaches to North Korea and over cost-sharing responsibilities.

Harris has several times been the object of controversy in the South, and accused of high-handedness. Even his facial hair became an issue of debate.

The envoy's mother was Japanese and, with Koreans still bitterly resentful of Tokyo's 1910-45 colonisation of the peninsula, commentators claimed the moustache alluded to the fashions of imperial governors-general from the period.

In January Harris retorted that his grooming was a matter of personal choice, and that his critics were "cherry picking history".

But over the weekend he uploaded a video to social media of him getting the moustache shaved off at a traditional Korean barbershop, saying he did so to keep cool in the Seoul summer, while wearing a mask to fight the coronavirus pandemic.

"Glad I did this," the envoy said in a tweet.

"For me it was either keep the 'stache or lose the mask. Summer in Seoul is way too hot & humid for both. #COVID guidelines matter & I'm a masked man!"

Seoul and Tokyo are both major US allies, democracies and market economies faced with an overbearing China and nuclear-armed North Korea, but are locked in bitter disputes over historical issues.

Earlier this year Harris said: "I understand the historical animosity that exists between both of the countries but I'm not the Japanese American ambassador in Korea, I'm the American ambassador to Korea.

"And to take that history and put it on me simply because an accident of birth I think is a mistake."