A widely circulated photo of Japanese Prime Minister Shinzo Abe in a military jet trainer drew flak in South Korea, where the image was said to reflect Japan’s colonial-era atrocities.

The face of a smiling Abe giving the thumbs up while sitting in the cockpit of an T-4 training jet with the number 731 evoked unwelcome memories of suffering under Japanese occupation and colonization, South Korean media said.

Chosun Ilbo, the largest daily in South Korea, described the photo as part of “endless provocation” from Japan. Korea JoongAng Daily ran the photo under the headline “Abe’s pose resurrects horrors of Unit 731”.

Unit 731 was a covert Japanese biological and chemical warfare research facility which carried out lethal human experiments during the Sino-Japanese War and World War II.

The Japan Defence Ministry claimed the number on the jet was simply coincidental.

“There was no particular meaning in the number of the training airplane the prime minister was in on Sunday,” a ministry spokesman told AFP in Tokyo.

The image triggered public anger in South Korea following the controversial visit of Japanese lawmakers to the Yasukuni war shrine which Seoul says aggravates the “scars of the past”.