Donald Trump once criticised Barack Obama for giving too much
Syrian forces and their allies are withdrawing from military bases likely to be targeted in a potential US airstrike.
Pro-Assad militants, and some Syrian government forces, are moving people and equipment out of the way ahead of an impending attack by the United States.
Satellite imagery also showed ten Russian warships and a submarine leaving a port in western Syria.
The clear-out came after President Donald Trump warned his foes to "get ready" for a US missile strike, apparently contradicting his former opinion that telegraphing military action is a big mistake.
In a tweet on Wednesday, Trump warned Russia that US missiles "will be coming, nice and new and 'smart!'"
There are potential advantages to telegraphing your actions — the main one being that it helps avoid accidental escalation in a busy conflict zone where Russia is also active.
On Thursday Trump also reintroduced some ambiguity, saying that the attack "could be very soon or not so soon at all!"