Mr Hammarskjold’s plane was travelling to Congo on a peace mission in 1961 when it crashed in Zambia.
A UN investigation in 1962 failed to find the cause of the mysterious crash.
The commission said there were significant new findings, and that America’s National Security Agency may hold crucial evidence.
The Swedish-born diplomat’s plane crashed on 18 September in a forest near Ndola in Northern Rhodesia, now Zambia.
All but one of the passengers and crew on the flight were killed.
Three investigations have failed to determine the cause of the crash, and many conspiracy theories have swirled around Mr Hammarskjold’s death.