Forces marshalling for Syria strike
ANY strike by the United States and its allies on Syria will probably aim to teach Syrian President Bashar Al-Assad - and Iran - a lesson on the risks of defying the West, but not try to turn the tide of the civil war.
US and European officials said a short, sharp attack - perhaps entirely with cruise missiles - is the preferred response to what they believe is Mr Assad's responsibility for a chemical-weapons attack on rebel-held areas last week.
If such a strike goes ahead, US President Barack Obama's administration will have to select its targets with extreme care.
Without some action soon, officials worry that Mr Assad will feel he can resort to chemical weapons again with impunity - a year after Mr Obama declared their use a "red line" that, if crossed, would incite strong action. Some also fear inaction in Syria could cast doubt over other US "red lines".
Choosing targets is fraught with danger. The most likely, officials say, would be Mr Assad's command-and-control facilities, air defences and any part of his chemical arsenal they believe can be attacked safely.
What must be avoided is any action that, while designed to punish the use of chemical weapons, perversely ends up releasing dangerous materials into the environment.
Defence sources said US commanders want overwhelming force and a robust regional coalition available to deter any Syrian retaliation.
Current and former Western officials, including those directly involved in policy, said Syria's sophisticated air defences and their worries about the risk of casualties among allied aircrew meant the cruise-missile strike was now most likely.
A "stand-off" attack could be launched from US warships, or aircraft firing missiles without entering Syrian airspace. The US said it now has four destroyers that carry cruise missiles in the Mediterranean.
Its most powerful ship in the region - aircraft carrier USS Harry S Truman - left the Mediterranean on Aug 18, passing south through the Suez Canal into the Red Sea, although it could still be within striking range.
Defence sources said Britain has kept an attack submarine in the Mediterranean for several months, allowing it to join any US-led missile barrage, just as it did with Libya.
The French carrier, Charles de Gaulle, has just been declared operational after a refit. Currently in the Mediterranean port of Toulon, it could be off Syria within three days.