South Korean national police guard the Takeshima islands in pairs positioned at various lookout points. (Chico Harlan/The Washington Post)

Web users in both Japan and South Korea are up in arms over Japanese celebrations on Friday of Takeshima Day — a quasi-official holiday designed, appropriately, to mark an old territorial spat between Japan and South Korea.

Takeshima, or Dokdo in Korean, are a string of uninhabited volcanic outcroppings in the Sea of Japan. Both Japan and South Korea claim them, a dispute going back at least 60 years. The holiday, for its part, only goes back six years, when a local Japanese council signed it into law "as hundreds of nationalists sporting paramilitary gear" urged it on.

This year, as in years past, the holiday remains divisive. Japan's central government sent a representative to celebrate in Shimane prefecture for the first time, reports the Wall Street Journal. Some 50 South Korean protesters gathered outside the Japanese Embassy in Seoul, and South Korea's foreign ministry promised to make a formal complaint.

Online commenters were less than sympathetic. The blog JapanCrush translated Japanese reactions from Twitter and other sites, most of which it calls "dismissive of Korean anger at ‘Takeshima Day.' "

"If you’re going to kick up a fuss, you’re welcome do it in your own country," one wrote, jokingly.

If nothing else, Takeshima Day remains a reminder that Japan and South Korea haven't always been friendly. Japan occupied the Korean Peninsula from 1910 to 1945 and has had, shall we say, "a poor image" there ever since, The Post's Anthony Faiola reported when the holiday was signed into law in 2005.

Much of the social media fury reflects that ongoing prejudice.

"They’re Koreans, aren’t they? It’s not so surprising," one user wrote. "They are Koreans, after all."