A United Nations inquiry into a 1961 plane crash that killed then-U.N. Secretary-General Dag Hammarskjold found that new information pointing to an aerial attack or threat bringing down the aircraft warrants further investigation.

Hammarskjold — a Swede elected as the world body's second chief in 1953 — was killed along with 15 others while on his way to broker a truce in Katanga in what is now Democratic Republic of Congo. The plane crashed in Northern Rhodesia, now Zambia.

"The panel ultimately found significant new information that it assessed as having sufficient probative value to further pursue aerial attack or other interference as a hypothesis of the possible cause of the crash," Secretary-General Ban Ki-moon wrote in a letter to the General Assembly released on Monday.