Indonesia has accused the Malaysian organisers of the Southeast Asian Games of negligence after the Indonesian flag was printed upside down in a souvenir guidebook.
The mistake, which makes the red-and-white Indonesian flag resemble Poland's, has caused anger in Indonesia where "shameonyoumalaysia" has become the most popular hashtag on Twitter.
Indonesia's Olympic Committee chairman Erick Thohir said the mistake "shows negligence" and demanded the guidebook be withdrawn and a new version printed.
"Friendship is the greatest legacy in sports, but a mistake in presenting a national identity is not justified," he said.
Indonesia appears to have taken particular offence because the guidebook was distributed to VIPs at Saturday's opening ceremony in Kuala Lumpur for the 29th Southeast Asian Games and only its flag was shown incorrectly.
Youth and Sports Minister Imam Nahrawi said the error was "very painful".
Malaysia and Indonesia are both Muslim majority nations and share a similar language but often trade accusations of stealing the other's food and culture.
The creation of Malaysia when the British empire was dismantled after WWII was bitterly opposed by Indonesia, itself then a new nation emerging from Dutch colonial rule and a short-lived Japanese occupation.
