Paul Moss

As our correspondent in Washington, Sean Dilley, explains.

Ahmad al-Sharah was once upon a time a sworn enemy of the United States.

The politics in Syria is, of course, very complex.

He was a rebel.

overthrowing Assad, the previous president in Syria.

So once upon a time, the two countries really would have had absolutely no love lost between them.

Last month, however, President Trump had welcomed the new Syrian president into the White House, into the fold.

He'd lifted sanctions on Syria, which had been crippling the country.

And the quid pro quo for that is the expectation that the US wants Syria to help out

lower that heat in the region with its neighboring countries in Israel.

So it's very important that this is seen as something that they're tackling together.

And that's why President Trump and Pentagon sources are saying there was an attack on U.S.

and Syrian forces.

In other words, the

very serious retaliation, to use the words that he has used, would be against those deemed responsible.

Donald Trump has said that he believes that would be ISIS, but certainly this isn't a question, as historically would have been the case, of potentially having to deal with a Syrian government.

So very much keeping the presidents of Syria in the tent on this one.

Sean Dilley.

The US Defence Secretary, Pete Hegzeth, responded to Saturday's shooting by saying...

if you target Americans anywhere in the world, the United States will hunt you, find you and ruthlessly kill you.