Media playback is unsupported on your device Media caption Senator Robert Menendez said ''al-Megrahi was released under false pretences''

A US Congressional inquiry into the release of Lockerbie bomber Abdelbasset al-Megrahi says there was strong political pressure on the Scottish government to free him.

It also casts doubt on the competence of the doctors who examined Megrahi.

"Commercial and economic considerations trumped... our global fight against terrorism," said Senator Bob Menendez.

The report comes on the 22nd anniversary of the bombing, in which 270 people died.

The investigation states that officials working under former British Prime Ministers Tony Blair and Gordon Brown continually pressured Scottish authorities to release Megrahi.

The Scottish government released Megrahi in August 2009 on compassionate grounds because he was diagnosed with terminal prostate cancer. He returned to Libya following his release and is still alive.

Image caption Megrahi was convicted of murdering 270 people in the 1988 Lockerbie bombing

A Scottish government spokesman rejected what it described as senators' "false interpretation".

"This is not an official report of the Senate foreign relations committee - it is an incorrect and inaccurate re-hash by four senators of material that has been in the public domain for many months...," a government spokesman said in a statement.

'False' medical prognosis

The senators' report states that Scottish authorities examining the former Libyan intelligence officer relied on "false" and "flawed" medical prognosis that may have been influenced by a doctor hired by the Libyan government.

Mr Menendez, along with three other senators, launched the investigation after officials from Scotland, the UK and BP did not testify at a Senate foreign relations committee hearing, he was scheduled to chair in July.

"This was a case in which commercial and economic considerations trumped the message of our global fight against terrorism," said Mr Menendez.

He added: "We have to make it impossible that anything like this injustice takes place again."

Mr Menendez is set to unveil the report - Justice Undone: The Release of the Lockerbie Bomber - at a news conference in Washington on Tuesday.

Megrahi was jailed in 2001 for the bombing of Pan AM flight 103 over Lockerbie which claimed 270 lives, in one of the deadliest terror attacks prior to 9/11.