A few provocative tidbits have emerged about the mysterious 1961 death of United Nations Secretary General Dag Hammarskjold, just months before the world body may forever close the book on the unsolved case.

The new information, which appears to corroborate the theory that South African or Belgian mercenaries may have forced the plane carrying Mr. Hammarskjold and 15 others to crash in a conflict region of Africa, is far from conclusive.

But it has provided more fuel for questions about what powerful nations may still be withholding in their intelligence archives about the crash, a defining event nearly six decades ago in emerging post-colonial Africa.

Mr. Hammarskjold, a pipe-smoking Swedish diplomat whose name now adorns buildings in and around the United Nations headquarters in New York, was on a mission to settle a conflict over Katanga, a rebellious part of Congo, when his aircraft, a chartered DC-6, crashed just after midnight on Sept. 18, 1961.