The US is repositioning its naval forces in the Mediterranean as it considers a military response to the alleged chemical-weapons attack near the Syrian capital, Damascus, that killed hundreds.
A US military source said on Friday that the US Navy was strengthening its fleet of cruise missile-carrying destroyers in the Mediterranean to four by delaying the return to the US of the Arleigh Burke class destroyer USS Mahan.
The aircraft carrier USS Harry S Truman, by far the most powerful warship in the region, left the Mediterranean last weekend, passing through the Suez Canal into the Red Sea.
Defence experts say the carrier's aircraft could strike Syria from south of Suez.
Several of the Truman's escort ships are also capable of launching Tomahawk land-attack cruise missiles.
Since earlier this year the US has had F-16 fighter jets based in Jordan.
French nuclear aircraft carrier Charles de Gaulle is in the Mediterranean port of Toulon. France has Rafale and Mirage fighters based in the United Arab Emirates.
Without an operational aircraft carrier, the UK would be dependent on its cruise missile-carrying Trafalgar and Astute attack submarines if it joined a US-led campaign.
