MacAskill could be summoned to Washington to testify on Megrahi

• Kenny MacAskill may be summoned to the US

Officials in Washington confirmed they want to ask UK ministers to give evidence about their handling of the case. Abdelbaset Al Megrahi, the only man convicted of the bombing of Pan Am Flight 103 in 1998, was released last year by Scottish ministers on compassionate grounds, following medical advice that he had three months to live.

Next month will mark a year since he was returned to Libya to a hero's welcome.

The US Senate Foreign Relations Committee also confirmed it will order officials from oil company BP to attend, following claims that the release of Megrahi was linked to British oil deals with Libya.

UK ambassador to the United States, Nigel Sheinwald, was forced to intervene in the row earlier this week, writing to the Senate Committee chairman John Kerry to insist claims of any link between Megrahi's release and oil deals were "untrue".

But First Minister Alex Salmond said yesterday that if Mr Kerry and his colleagues wanted to find the full facts, they should call Tony Blair to give evidence.

Mr Salmond cited the "deal in the desert" made by Mr Blair and Libyan leader Colonel Gaddafi in 2007, when the two leaders agreed plans to open up the country to foreign trade.

The inquiry will be chaired by New Jersey Senator Robert Menendez who said he wants to examine the "full circumstances" around Megrahi's release.

As to who will be asked to testify, a spokesman for the senator said aides were examining whether they could ask foreign government ministers to attend.

The spokesman added: "We are looking into this. You can't compel a foreign government to testify but it is on a preliminary list (of witnesses]."

The spokesman confirmed officials from BP and the US State Department will be called to put their side of the story. Scottish and UK ministers will likely be informed next week whether they have been asked to come to Washington.

A Scottish Government spokeswoman said: "The issues being raised in the United States at present regarding BP refer to the Prisoner Transfer Agreement negotiated by the governments of the UK and Libya, and have nothing to do with the decision on compassionate release.

"Nonetheless, we would always look to assist any properly constituted inquiry."

Officials have pointed out that Mr MacAskill rejected Megrahi's release under the Prisoner Transfer Agreement and that he never had any contact with BP prior to his decision.

Scottish ministers opposed the signing of the transfer agreement which was drawn up by the Libyan and UK governments without Edinburgh's consent.

But victims' families say they believe BP oil deals with Libya did factor in the decision to release him.It follows revelations since Megrahi's release about Libya-UK trade links.

Former Justice Secretary Jack Straw has admitted that when he was deciding whether to include Megrahi in the Prisoner Transfer Agreement with Libya, as requested, trade deals were a crucial factor.

Mr Menendez said yesterday: "For our national security and for fundamental justice, we need answers about the circumstances of this convicted terrorist's release, and we intend to get answers at this hearing."