A South Korean man is under investigation for hurling a bottle of human feces into Japan's Embassy in Seoul in anger over Tokyo's claims to South Korea's easternmost islets of Dokdo, police said Saturday.

The 49-year-old day worker threw the 750-milliliter plastic bottle containing his own feces over the wall of the embassy in central Seoul around 8:50 p.m. Friday after Japan held an annual event claiming its sovereignty over Dokdo earlier in the day.

The man from the southeastern city of Ulsan, identified only by his surname Choi, was immediately taken into police custody. After questioning, police booked him without physical detention for investigation, officials said.

Choi has a track record of anti-Japanese protests.

In August last year, he also threw a bottle of human feces into the embassy in anger over Japan's sovereignty claims to the East Sea islets. In 2010, he cut off part of his little finger and sent it to the embassy by mail for the same reason.

On Friday, Japan's Shimane Prefecture held its annual "Takeshima Day" event, Japan's name for the islets, aimed at bolstering its claims over Dokdo. This year's event was larger in scale as a central government official attended the event, along with 21 lawmakers.

Seoul filed a strong protest, calling Japan's claims "unjustifiable."

South Korea has rejected Japan's claims to Dokdo as amounting to denying Korea's independence from its 1910-45 colonial rule because the country reclaimed sovereignty over its territory, including Dokdo and many other islands around the Korean Peninsula, when it regained independence.

South Korea has kept a small police detachment on Dokdo since 1954. (Yonhap News)