The United States plans to unseal charges soon against a Libyan man suspected of assembling the bomb that blew up a US airliner over Lockerbie, Scotland, in 1988, US newspapers have reported.
But in Britain, the father of one of the victims of the disaster called the development "unwelcome" and cast doubt on the involvement of the suspect, Abu Agila Mohammad Masud.
"I can't see the connection between these new allegations and the Lockerbie story," Jim Swire, whose daughter Flora was killed in the bombing 32 years ago, told AFP on Thursday.
Masud is currently being held by the Libyan authorities, according to The Wall Street Journal, and US authorities are seeking his extradition to stand trial in the United States.
The New York Times said Masud's exact whereabouts are unknown but that he was imprisoned in Libya at one point for unrelated crimes.
The Journal said Masud, alleged to have been a top bomb-maker for the late Libyan leader Moamer Kadhafi, is suspected of assembling the device that blew up Pan Am Flight 103.
The newspapers said US prosecutors are expected to unseal charges soon against Masud.
The case against Masud is reportedly based largely on a confession he gave to Libyan authorities in 2012 as well as travel and immigration records.
Monday is the 32nd anniversary of the bombing which killed a total of 270 people, including 190 Americans and 11 people on the ground.
The FBI said that while it "cannot comment on any upcoming announcement, we can assure the public and most importantly, the families of the Pan Am 103 victims, that we have worked tenaciously for 32 years to investigate this horrific terrorist attack."
"Domestic and foreign partners alike have been focused on identifying who was responsible for the bombing," it added.
"Just as in any investigation, the FBI is persistent in our investigations with a dedicated focus on the victims of crime and terrorism."
- Scottish appeal -
Five judges at Scotland's highest court of criminal appeal are currently considering a posthumous appeal by the family of the only man convicted of the bombing.
Former Libyan intelligence officer Abelbaset Mohmet Al-Megrahi was convicted at a Scottish court sitting in the Netherlands in 2001 and jailed for life for mass murder.
But he maintained his innocence until his death in 2012. His family this year won the right to challenge his conviction on the grounds of "unreasonable verdict" and the withholding of evidence from his defence team.
The family's lawyer, Aamer Anwar, questioned the timing of the US announcement.
"Of course we doubt the motivation of the American authorities," Anwar said, noting that if the verdict against Megrahi was overturned, the whole case against Libya would collapse.
It has long been claimed that Iran used a Syria-based Palestinian proxy to build the bomb that downed the Boeing 747 as it travelled from London to New York.
Iran is said to have wanted revenge for a US Navy strike on an Iranian Airbus six months earlier in which 290 people were killed.
Anwar questioned the involvement of outgoing US Attorney General Bill Barr, who first announced charges against Megrahi and his co-defendant Amine Khalifa Fhimah, who was acquitted, in 1991.
"What exactly has he (Barr) been doing and why do it a few days before the anniversary?" he asked.
Swire, who is convinced of Megrahi's innocence and is backing his family's appeal, also said he was concerned the US charges could interfere with the Scottish case.
"(It) makes it all the harder for their lordships to be objective about what they're doing," he said.
Swire has said he does not believe Libya was involved in the bombing but that he and the other families of the victims wish to see justice done, whoever the perpetrators might be.
"If they really have some valid evidence against this man (Masud), no one would be happier than me to see the issue tried in a court where the evidence provided to that court was objective and on a level playing field," he said.
He added he was motivated ultimately by the memory of his daughter. "I think she would have wanted the truth to be known about whose hand it was that had murdered her," he said.