The British, US and Libyan governments have vowed to work together to reveal the full facts of the Lockerbie bombing which claimed 270 lives.
The announcement came in a joint statement as memorial events were held in the UK and United States on the 25th anniversary of the tragedy.
The statement by the three administrations said they wanted "all those responsible for this most brutal act of terrorism brought to justice".
Libyan Abdelbaset al-Megrahi was the only person convicted of the bombing of Pan Am flight 103 on 21 December 1988.
He was released from jail by the Scottish government on compassionate grounds after being diagnosed with prostate cancer, and died last year protesting his innocence.
In the US, a ceremony took place at the memorial cairn in Arlington National Cemetery, near Washington DC.
Syracuse University, in New York state, lost 35 students who had been studying at its London campus. A service of "hope and remembrance" was being held at the university's chapel.
A wreath-laying and church service was held on Saturday in the south of Scotland town which was devastated when the airPan Am flight 103 was blown from the skies on 21 December 1988.
Scotland's First Minister Alex Salmond and Lord Wallace, Advocate General for Scotland, were among those who took part in the ceremony at Dryfesdale Cemetery.
Other gatherings marking the anniversary of Britain's worst-ever terrorist attack included a remembrance service at Westminster Abbey in London.
The Lockerbie bombing remains the deadliest act of terrorism ever committed in the UK and until the attacks of 9/11 it was also responsible for the biggest single loss of American lives in such an attack.
All 243 passengers and 16 crew died, and a further 11 people were killed in their homes when wreckage hit the ground in Lockerbie.
The majority of the passengers and crew on board the aircraft were US citizens.