The United States says the repatriation of Red Army hijackers is one of the conditions for a possible removal of North Korea from Washington's list of terrorism-sponsoring nations.

The State Department's remarks follows a Japanese Foreign Ministry announcement that it has started negotiations with Pyongyang on the unconditional return of the four hijackers.

Nine members of the Japanese Red Army hijacked the Yodo passenger jet in 1970 and landed in Pyongyang. The other hijackers have since died or returned to Japan. The remaining four recently sent a letter to the North Korean government expressing their wish to return to Japan.

The U.S. State Department re-designated North Korea as a terrorism-supporting nation in late April, citing the Stalinist state's abduction of Japanese nationals in the 1970s and 80s as well as its failure to return the four hijackers to Japan.