Trump warns he'll 'wipe out' Turkey's economy if Syria op turns 'inhumane'

US President Donald Trump has said that he hoped Turkey would "act rationally" as the country launched an operation to invade the Kurdish-controlled North Syria.

Warning of actions against Turkey's economy, Trump said that he would consider moves tougher than sanctions if Ankara does not do the operations in northern Syria in as humane a way as possible.

"I will wipe out (Turkey's) his economy if that happens, Trump told reporters at the White House when asked if he is concerned that the Turkish President Recep Tayyip Erdogan will try to wipe out the Kurds.

Turkey has launched a broad assault on Kurdish-controlled areas in northeastern Syria, with intensive bombardment paving the way for a ground offensive.

The operation was possible after the White House announced late Sunday that Turkey would soon carry out a military operation in northern Syria and that US troops will no longer be in the immediate area.

Trump said he hoped Turkey President Erdogan would act rationally in terms of the operation in northern Syria.

I will tell you that I do agree on sanctions, but I actually think much tougher than sanctions if he doesn't do it in as humane a way as possible. (Senator) Lindsey Graham and I feel differently. I think Lindsey would like to stay there for the next 200 years and maybe add a couple hundred thousand people every place. But I disagree with Lindsey on that, he said.

When asked about humane way, the president indicated that he will adopt a policy of wait and watch.

We are going to have to see. We're going to have to define that as we go along. If you listen to Erdogan, he wants to have people go back to where they came from, go back to Syria, he said.

"Right now, Turkey is holding millions of people that would be all over the place if Erdogan wasn't holding them. So, he wants to repatriate. He wants to have them to go back into the area that he's looking at," he said.

"We will see. We'll see how he does it. He could do it in a soft manner. He could do it in a very tough manner. If he does it unfairly, he's going to pay a very big economic price, Trump warned.