said Wednesday it has received an envelope containing a threatening letter and what appears to be a human finger.
The envelope, received Saturday at the pro-Pyongyang group's head office in Chiyoda Ward, Tokyo, was addressed to Chongryun Chairman So Man Sul, the group said, calling it "an aberrant and insidious criminal act."
Tokyo police said they are investigating whether the object, which appears to be a pinkie, is real, and is trying to determine the sender.
Chongryun said it opened the letter in the presence of police Tuesday, because the name of the sender indicated the letter was from the leader of a rightwing group.
The envelope was postmarked in Kagoshima Prefecture. Inside were two smaller envelopes -- one with the letter and the other with a fingerlike object wrapped in gauze, police said.
The three-page letter bears the hand-written phrase "punishment from heaven" and condemns North Korea's abductions of Japanese and its test-firings of ballistic missiles, the police said.
On Tuesday, Chongryun demanded that Japan remove all sanctions imposed on North Korea since the missile firings on July 5, including financial sanctions Tokyo imposed earlier the same day.