Forces which could be used against Syria:
Four US destroyers - USS Gravely, USS Ramage, USS Barry and USS Mahan - are in the eastern Mediterranean, equipped with cruise missiles. The missiles can also be fired from submarines, but the US Navy does not reveal their locations
Airbases at Incirlik and Izmir in Turkey, and in Jordan, could be used to carry out strikes
Two aircraft carriers - USS Nimitz and USS Harry S Truman are in the wider region
French aircraft carrier Charles de Gaulle is currently in Toulon in the western Mediterranean
French Rafale and Mirage aircraft can also operate from Al-Dhahra airbase in the UAE
BBC News - Russia's Vladimir Putin challenges US on Syria claims