British Prime Minister David Cameron has attacked the release of the only man convicted of the Lockerbie bombing in 1988, ahead of an official visit to the United States.
The Scottish government last year freed Abdelbaset al-Megrahi on compassionate grounds, because he has terminal cancer because it believed he had only three months to live. He is still alive.
The US Congress is investigating the decision to free him.
Mr Cameron says he doesn't understand why al-Megrahi was released.
Two hundred and 70 people died in the bombing of an a Pan Am airliner above the Scottish town of Lockerbie.