Photos of the handwritten sign saying "lavatory for crew members only" went viral in South Korea this week after a passenger on a 10-hour flight from Amsterdam to Seoul's Incheon airport on Monday shared the images online.

Netizens call KLM Royal Dutch Airlines racist after posting this sign in Korean https://t.co/V7XpJXdnRm pic.twitter.com/Mw2zZBSNVI

— allkpop Buzz (@allkpopBuzz) February 12, 2020

The passenger accused KLM of discriminating against South Korean passengers because the sign was only in Korean.

"Dear KLM... Today, you made it quite clear that you discriminate against race. Using Corona Virus as an excuse. You owe my friend and Korea a HUGE apology," wrote one Twitter user, whose posts in English and Korean about the incident gathered thousands of retweets and likes.

The hashtag BoycottKLM was trending on Korean Twitter.

On Friday, executives with KLM bowed as they publicly apologised at a news conference in Seoul, saying they take allegations of discrimination "very seriously" and promising to prevent it from happening again.

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"This is a human mistake, and we don't take it lightly," said Guillaume Glass, an Air France-KLM regional general manager. "We are deeply sorry that this was viewed as discrimination, which was absolutely not the intention of the crew."

The crew said using only Korean on the sign was simply an oversight. An English notice was added after passengers complained, Glass said.

It is not KLM policy to reserve lavatories for crew, he added.

On Wednesday, South Korea's transportation ministry released a statement warning KLM over its "discriminatory measures" and calling on the company to ensure it didn't happen again.

At a previously scheduled meeting on Friday, Dutch Ambassador Joanne Doornewaard expressed regrets over the incident to Transportation Minister Kim Hyun-mee, a ministry official told Reuters.