Cameron told BBC television on Monday he opposed the Scottish government's decision to return the cancer-stricken prisoner to Libya on compassionate grounds last August.
Ahead of a visit to the United States beginning Tuesday, Cameron said the decision was "completely and utterly wrong."
U.S. Sen. Charles Schumer and others have called for an inquiry into oil giant BP's lobbying of the British government over a prisoner transfer agreement with Libya.
Cameron, who took office in May, said he had "no idea what BP did" in lobbying the previous government. Cameron's office insisted talks did not relate to the al-Megrahi case.
