The United States on Friday slammed the release of Lockerbie bomber Abdelbaset Ali Mohmet al-Megrahi from a Scottish prison one year ago as "unfortunate, inappropriate and wrong." The comments from President Barack Obama's counter-terrorism adviser, John Brennan, came after US Secretary of State Hillary Clinton said Washington "continues to categorically disagree with the decision" to free Megrahi. "As we have expressed repeatedly to Scottish authorities, we maintain that al-Megrahi should serve out the entirety of his sentence in prison in Scotland," Clinton said in a statement. "We have and will continue to reiterate this position to the Scottish and Libyan authorities. We extend our deepest sympathies to the families who lost loved ones and share their desire for justice to prevail," she said. The remarks from Brennan and Clinton came amid calls from four US senators for a new investigation into whether business considerations played a role in the decision to let Megrahi return to his homeland of Libya. The lawmakers have suggested that embattled oil giant BP might have lobbied for his release in order to safeguard a 900-million-dollar oil exploration deal with his Tripoli, a charge Scottish and British officials have denied. Megrahi was thought to have only three months to live because of terminal prostate cancer when he was released on compassionate grounds and returned to his homeland Libya to a hero's welcome -- but has confounded that diagnosis. Megrahi remains alive today, to the dismay of mainly American relatives of the 270 people who died when Pan Am Flight 103 blew up over the Scottish town of Lockerbie, four days before Christmas in 1988. Brennan spoke to reporters on the resort island of Martha's Vineyard, where Obama was spending a 10-day vacation from Washington with his family.