The 270 victims of the Lockerbie bombing have been remembered on the 25th anniversary of the atrocity.
Memorial events were held in the town of Lockerbie in southern Scotland, at Westminster Abbey in London and at Arlington National Cemetery in the US.
Many of those who attended a wreath-laying ceremony and church service in Scotland came from the US, where most of the victims where from.
Meanwhile, the UK and US governments vowed to "deepen" their cooperation with Libya in the hope of learning more about how and why the bombing happened.
ITV News' Scotland Correspondent Debi Edward reports from Lockerbie:
Messages of condolence came from politicians around the world, led by Scotland's First Minister Alex Salmond who said that: "Out of disaster, there are the bonds of friendship.''Lockerbie has been a welcoming place for the relatives of those who died, and over the last 25 years has taken as good care of people as it possibly could."
The Prime Minister left his own message on Twitter:
As we mark 25 years since the Lockerbie tragedy, my thoughts are with those who lost loved ones so close to Christmas.
Labour leader Ed Miliband called the bombing a "horrific act of terrorism that cruelly took the lives of people from Lockerbie, the rest of the UK, the USA and across the world".
The remembrance service at Dryfesdale Church in Lockerbie was led by students from a scholarship programme between Lockerbie Academy and Syracuse University in the US.
Of the 259 people travelling on the Pan Am flight, 35 were students from Syracuse.
Meanwhile at Westminster Abbey, Dr Jim Swire, whose daughter Flora died in the disaster, called on people to pray for the family of Abdelbaset al-Megrahi, the only man convicted of the attack.
A minute's silence was observed at the services at 7pm to coincide with the moment the bomb exploded.
Pan Am flight 103 was on its way from London to New York when it exploded above Lockerbie, on the evening of December 21 1988, killing everyone on board and 11 people on the ground.
Libyan security professional al-Megrahi was found guilty in January 2001 and given a life sentence.
He was diagnosed with prostate cancer in 2008, leading to a decision to free him under compassionate release rules.