Britain, the United States and Libya have issued a joint call for justice over the Lockerbie bombing as services were held to mark the 25th anniversary of the attack, which claimed 270 lives.

The three governments gave their “deepest condolences” to relatives of those who died when Pan Am Flight 103 blew up over the Scottish town of Lockerbie on December 21, 1988, en route from London to New York.

All 259 people on board – most of them Americans heading home – were killed as well as 11 people on the ground.

“We want all those responsible for this most brutal act of terrorism brought to justice, and to understand why it was committed,” the governments said in a statement.

“We are committed to co-operate fully in order to reveal the full facts of the case.”

Only one person has ever been convicted over the bombing – Libyan Abdelbaset Ali Mohmet al-Megrahi, who died last year still protesting his innocence.

Scotland’s leader Alex Salmond was among the mourners laying wreaths on Sunday at Lockerbie’s Dryfesdale Cemetery, which houses a memorial to the victims.

“On this 25-year anniversary, and as the country prepares once more to relive the harrowing events of that terrible night, it is important that we remember that the pain and suffering of the families and friends of those who died has endured since that winter night in 1988,” Salmond said.

US Attorney General Eric Holder and Scottish officials attended a memorial service at Arlington National Cemetery just outside Washington.

“We will always remember the heartache, the devastation and the pain that was etched into our collective memory on the 21st of December, 1988,” Holder said.

“We keep calling for change and fighting for justice, on behalf of those no longer with us.”

Syracuse University in New York, which lost 35 students in the bombing, also held a remembrance ceremony during which a peace prayer was read.

Hundreds of mourners, including senior politicians and friends and families of victims, gathered at London’s Westminster Abbey.

Libya admitted responsibility for the bombing in 2003 and the regime of slain dictator Muammar Gaddafi eventually paid $US2.7 billion ($A3.06 billion) in compensation to victims’ families as part of a raft of measures aimed at a rapprochement with the West.