The top US military officer has outlined the costs, risks and benefits of possible American military involvement in the Syrian conflict.
Joint Chiefs of Staff chairman Gen Martin Dempsey offered five military options, including limited strikes and establishing a no-fly zone.
But he said using force in Syria would be "no less than an act of war" and could cost the US billions of dollars.
Washington has so far ruled out military intervention in Syria.
Its role in the conflict is currently limited to delivering humanitarian aid to Syrian refugees in neighbouring countries and providing non-lethal help to the Syrian opposition.