The circumstances under which Masud was taken into custody by the USA initially remained unclear. When charges were brought against him in the United States two years ago, he was in custody in Libya for his alleged involvement in the attack on the Berlin nightclub "La Belle" in 1986, in which two US soldiers and a Turkish woman were killed died. The British broadcaster BBC reported last month that Masud had been kidnapped by a Libyan militia.

A spokesman for the US Department of Justice said Masud is expected for a first hearing in federal court in Washington. He didn't give a date but said details would be announced shortly. According to a report in the New York Times, Masud was arrested by the FBI and is currently being extradited to the United States.

Masud has been under investigation in the USA and Scotland for years. The ex-agent is suspected of having built the bomb for the Lockerbie attack. The attack on a US passenger plane 34 years ago killed 270 people, including 190 US citizens. The Pan Am airliner was en route from London to New York on December 21, 1988 when it exploded over the small Scottish town of Lockerbie 38 minutes after take-off.

So far, only one person has been convicted of the Lockerbie attack: in 2001, former Libyan intelligence officer Abdelbaset Mohamed al-Megrahi received a long prison sentence, but was released from a Scottish prison in 2009 on medical grounds and died in 2012 in the Libyan capital, Tripoli. He maintained his innocence until his death.

The Scottish public prosecutor's office said it was determined to continue investigating with the police and in coordination with the US authorities "to bring to justice those who acted alongside al-Megrahi".

The Lockerbie attack was the deadliest attack ever carried out on UK territory. Libya took responsibility in 2003 and paid $2.7 billion in compensation to the victims' families.

The investigation picked up steam again in 2016 when Washington learned of Masud's arrest after Gaddafi's ouster in 2011 and his alleged confession to the new Libyan government in 2012.