A South Korean civic group on Friday placed a half-page advertisement in one of China's influential state-run newspapers, promoting the Korean name of the "East Sea," the body of water that separates South Korea and Japan.

South Korea and Japan have locked horns for decades over the name of the body of water, with Seoul calling it the "East Sea" while Tokyo uses the name "Sea of Japan." The ad in the Beijing Youth Daily was published while Chinese President Xi Jinping is on a two-day state visit to Seoul.

Headlined "Do You Know?" the ad said that the body of water between South Korea and Japan "has been called 'East Sea' for 1,000 years."

"A lot of evidence is found in old maps of China and Europe," the group said, adding that the ad was sponsored by "a South Korean civic group."

It was the first time that the official newspaper of China's ruling Communist Party ran an ad on the East Sea naming.

The naming issue is particularly sensitive for Seoul as Tokyo has continually stepped up efforts to claim the South Korean islets of Dokdo in the East Sea. South Korea keeps a small police detachment on the volcanic outcroppings.

Korean historians and experts believe the sea's original name was the East Sea, but that the term Sea of Japan became more widely adopted because Korea failed to properly counter Japan's campaign to change the name due to colonization by Japan and the 1950-53 Korean War. (Yonhap)