Libyan army forces unload supplies from a Chinook helicopter at a border crossing station in western Libya

Libyan army forces unload supplies from a Chinook helicopter at a border crossing station in western Libya March 1, 2011. Libya could descend into civil war if Muammar Gaddafi refuses to quit, the United States said on Tuesday, its demand for an end to his rule carrying new weight after word of unspecified Western military preparations. But the veteran Libyan leader remained defiant, sending forces to a western border area amid fears that the most violent Arab revolt may grow more turbulent and trigger a regional humanitarian crisis. REUTERS/Yannis Behrakis (LIBYA - Tags: CIVIL UNREST POLITICS MILITARY)