UNITED NATIONS: A United Nations inquiry into a 1961 plane crash that killed then 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.

The three-member panel asked for specific information from Belgium, France, Germany, South Africa, the United States and Britain during its three-month inquiry into the September 1961 crash, but said not all requests were entirely satisfied.

The panel said its ultimate conclusion was that to establish the "whole truth" the United Nations needed access to "classified material and information held by Member States and their agencies that may shed further light on this fatal event and its probable cause or causes."

Ban has asked his chief legal counsel to follow up with states "on the unfulfilled aspects of the panel's requests." Ban agreed that further investigation would be need to establish the facts of the plane crash.

Several theories have surrounded the death of Hammarskjold, who was posthumously awarded the Nobel Peace Prize in 1961.

The panel said new details related to claims by mercenaries and others that they shot down the plane lacked credibility, while a claim about possible sabotage using explosives was only "weakly supported." A hijacking theory was not supported.