The investigation into the 1988 bombing of a US-bound airliner over Lockerbie in Scotland is closed and Tripoli will not release more evidence that could lead to others being charged, Libya's interim leaders said.
The British Foreign Office, however, said the investigation into the bombing "remains open".
Scottish prosecutors had asked Libya's National Transitional Council (NTC) to give them access to papers or witnesses that could implicate more suspects, possibly including deposed leader Muammar Gaddafi.
Libya's interim justice minister Mohammed al-Alagi turned them down, telling reporters: "The case is closed."
But the Foreign Office in London said it had talked with the NTC tonight and it had promised continued cooperation.
"NTC chairman Mustafa Abdul Jalil has already assured the Prime Minister that the Libyan authorities will cooperate with the UK in this and other ongoing investigations," a Foreign Office spokesman said.
"Having spoken with the NTC this evening, we understand that this remains the case. The police investigation into the Lockerbie bombing remains open and the police should follow the evidence wherever it leads them."
Former Libyan agent Abdel Basset al-Megrahi was convicted of the bombing in 2001 and sent to a Scottish prison to serve a life sentence.
The Scottish government released him and sent him back to Libya on compassionate grounds in 2009 because he had cancer and was thought to have only months to live.
His release and return to a hero's welcome in Libya angered many in Britain and the US, home to most of the victims.
NTC fighters move on Sirte
Meanwhile, Libyan provisional government forces backed by NATO warplanes closed in on Muammar Gaddafi loyalists holed up in one of the last two bastions of the deposed leader.
Thick, black smoke billowed into the air as NTC fighters battled loyalist troops at a roundabout about 2kms from the centre of Sirte.
The advance in Sirte came two days after anti-Gaddafi fighters west of the city drove to within a few hundred metres of its centre before pulling back yesterday to make way for NATO strikes.
On the western edges of Sirte today, NTC fighters and Gaddafi loyalists traded heavy machine gun fire, rocket-propelled grenades and artillery rounds.
Sirte lies between Tripoli and the eastern city of Benghazi, both now held by the NTC whose rebel fighters overran the capital five weeks ago after six months of fighting.
Taking Sirte would be a huge boost for the NTC, which is trying to establish credibility as a government able to unite Libya's fractious tribes and regions, and a blow for Col Gaddafi, who is widely believed to be in hiding somewhere in Libya.
Humanitarian organisations have raised the alarm over conditions for civilians cut off in Sirte and in Bani Walid to the south.
Scores of civilians in cars laden down with personal belongings continued to stream out of the town to both the east and west.
NTC fighters checked them, looking for wanted figures among those who were, and may still be, loyal to Gaddafi.
Over 1,200 bodies found in Libyan mass grave
Libya's National Transitional Council says it has discovered a mass grave in Tripoli containing more than 1,200 bodies.
They are believed to be the remains of inmates who were killed by security forces in 1996 in the Abu Salim prison in the capital.
The mass grave was the first physical evidence revealed so far of the Abu Salim prison massacre, an event that was covered up for years but created simmering anger that ultimately helped bring about Colonel Muammar Gaddafi's downfall.
According to accounts from survivors who have spoken to human rights groups, starting at dawn on 29 June 1996, guards lined up inmates in the courtyards of Abu Salim.
Security men, standing on the prison rooftops, fired at the inmates with Kalashnikov rifles before using pistols at close range to finish them off.
