US warns Britain against leaving EU

“Britain is such a special partner of the United States — that shares our values, shares our interests, has significant resources to bring to the table. More than most others, its voice within the European Union is essential and critical for the United States,” Gordon added.

Gordon's comments come ahead of Prime Minister David Cameron's speech redefining the country's relationship with the 27-member body.

Cameron is under pressure at home to negotiate a looser relationship with the E.U., which is battling a debt crisis that has further enraged a traditionally eurosceptic public. The U.S. has vocally pushed for greater European integration since after World War II, both to stave off future wars and as a free-market bulwark against the Soviet Union.