Scotland's top prosecutor joined the director of the FBI on a mission to Libya to discuss the investigation into the Lockerbie bombing.
The Crown Office confirmed that Frank Mulholland and Robert Mueller were in Tripoli last week.
Abdelbaset Ali al-Megrahi was convicted in 2001 of carrying out the bombing, which killed 270 people.
He was returned to Libya on compassionate grounds in August 2009 after serving 10 years in jail.
In December last year, Mr Mulholland met Mr Mueller and US attorney general Eric Holder to discuss the opportunities for stepping up the investigation in Libya into the bombing.
At the time, the lord advocate said: "I think I would be failing in my duty if I didn't properly seek to take advantage of the opportunity that has opened up with the fall of Gaddafi.
"I am determined to get the answers these families deserve."
The Transitional National Government in Libya - which was borne out of the fall of the Gaddafi regime - told the Foreign Office at the end of last year it would allow police from Dumfries and Galloway to travel to the country to continue their probe into the bombing.
Megrahi is the only person to have been convicted in connection with the 1988 attack, which saw flight Pan Am Flight 103 blown up over the Scottish town of Lockerbie.
He was released by Scottish Justice Secretary Kenny MacAskill after being diagnosed with prostate cancer, and was allowed to return to Libya.
Megrahi has always spoken of his innocence.
Following Mr Mulholland's visit last week, a spokesperson for Crown Office and Procurator Fiscal Service said: "The Libyan authorities confirmed that they fully understood the importance of dealing with the tragic issues left behind by Colonel Gaddafi and his regime, both in Libya and overseas.
"The lord advocate expressed his desire to the Libyan prime minister that there will be a positive response to his recent request for co-operation and the International Letter of Request (ILOR)".