<br/>The United States has raised concerns about the release of the Lockerbie bomber, after the foreign secretary William Hague has said the decision to free him was a mistake. <br/>He spoke to US Secretary of State Hillary Clinton, who said Britain may wish to explain the circumstances behind Abdelbaset al-Megrahi's release. <br/>Four US senators believe oil giant BP lobbied for the move to secure a deal with Libya. The Scottish Government said Megrahi was freed on human grounds. It has denied having any contact with BP before its decision last year to release the Libyan intelligence officer convicted of the 1988 bombing, which killed 270 people, most of them Americans.<br/>