The father of American college student Otto Warmbier who died soon after being sent home from North Korea in a vegetative state says Kim Jong Un should be called "criminal Kim" — not "chairman Kim" which "makes me sick."

Fred Warmbier told a U.N. symposium promoting international cooperation on abductions Friday that calling North Korea's leader "chairman" gives him status on the world stage, and "if we're afraid to tell the truth of who we're dealing with we don't stand a chance of making a difference."

"Every member of Kim's regime is a thug," Warmbier said. "He's a criminal and he's a murderer."

During the meeting, relatives of abductees from Japan, Thailand and the U.S. whose loved ones are believed to be held in North Korea pleaded for their return.