The US is due to unseal charges against a Libyan man suspected of making the bomb that blew up Pan Am Flight 103 over Lockerbie in 1988, US media say.
US prosecutors will soon seek the extradition of Abu Agila Mohammad Masud to stand trial in the US, reports say.
He is currently being held in Libya, according to the Wall Street Journal. This has not been confirmed by the Libyan authorities.
The blast on board a Boeing 747 over the Scottish town left 270 people dead.
Most of the victims on board the flight from London to New York were American citizens.
It remains the deadliest terrorist incident ever to have taken place on British soil.
Libyan national Abdelbaset al-Megrahi was the only man convicted, in 2001, over the bombing.
Megrahi, who always proclaimed his innocence, unsuccessfully appealed against his 27-year sentence.
However, he was released from prison in Scotland and allowed to return to Libya on compassionate grounds in 2009 after it emerged that he had terminal cancer.
Megrahi died three years later, but a Scottish court is now considering a posthumous appeal against his conviction by his family.
What are US media reporting?
The US Department of Justice is expected to unseal a criminal complaint against Abu Agila Mohammad Masud in the coming days, the Wall Street Journal is reporting quoting senior department officials.
It says this will open a new chapter in one of the world's longest and most sprawling terrorism investigations.
The new charges are expected to be announced by outgoing US attorney-general, William Barr.
He held the same position when the US announced its first charges against Megrahi and another Libyan suspect, later acquitted, almost three decades ago.
"We will not rest until all those responsible are brought to justice. We have no higher priority," Mr Barr said at the time.
The Wall Street Journal reports that Mr Masud is being held in Libya, although the New York Times says his exact whereabouts are unknown. But it adds that he was jailed in Libya at one point for unrelated crimes.
Mr Masud is alleged to have been a top bomb-maker for late Libyan dictator Muammar Gaddafi.
Neither the US justice department nor the Libyan authorities have publicly commented on the issue.
https://www.bbc.com/news/world-us-canada-55337459
