The protest came the day Japan began releasing treated radioactive water from the wrecked power plant into the Pacific Ocean, a polarising move that prompted fresh, fierce criticism from around the region.

The group, made up mostly of young people, reached the eighth floor, where the embassy is located, and hung banners condemning the release.

“The sea is not Japan’s trash bin,” read one of the banners. “Stop releasing contaminated water at once.”

A Reuters photographer on the scene saw police officers physically carry and drag protesters from the building and bundle them into a bus.

A police officer at the Jongno police station in the capital said he did not have immediate information.

A protest organiser, who sought anonymity, told Reuters 14 people were detained. The Yonhap news agency put the number at 16.

About 50 people had gathered outside the embassy for the protest.