President Donald Trump said in a tweet yesterday that he had never telegraphed the timing of an attack on Syria, and that such a strike - for which he put Russia and Syria on notice just a day earlier - "could be very soon or not so soon at all!"

"In any event, the United States, under my administration, has done a great job of ridding the region of ISIS," Mr Trump said on Twitter, referring to the Islamic State in Iraq and Syria militants. "Where is our 'thank you, America?' "

France said yesterday it had proof the Syrian regime had used chemical weapons. The Trump administration is trying to coordinate its response with other allies, including France and Britain.

Syria has moved military aircraft to the Russian base near Latakia, and is working to protect important weapons systems.

SEE WORLD: Trump muddies the waters over timing of threatened Syria strike