Trump defends Syria pullout, says US cannot be the world's policeman

America cannot be the policeman of the world, US President Donald Trump has said during his first visit to Iraq as he urged other countries to share responsibilities.

Trump, on a surprise visit to US troops stationed in Iraq, defended his decision to pull American troops out of war-torn Syria, saying there would be no delays.

"The United States cannot continue to be the policeman of the world," Trump told reporters at a military base west of Baghdad, soon after he addressed American soldiers.

This is his first visit to Iraq as the US President. He is accompanied by First Lady Melania.

Trump vowed for a "harsh response" from his administration if there was to be another terrorist attack on America.

"If anything should happen at all, nobody will ever have suffered the consequences they had suffered," Trump told American troops at a military base west of Baghdad.

"It's not fair when the burden is all on us, the United States," he said, as he defended his decision to withdraw troops from Syria and let regional countries, Turkey in particular, to complete the work of finishing the remnants of the ISIS terror group and Saudi Arabia to invest in development of the war-ravaged country.

In his interaction with reporters, Trump described how he gave "the generals" multiple six-month "extensions" to get out of Syria.

"They said again, recently, can we have more time? I said, 'Nope'. You can't have any more time. You've had enough time. We've knocked them out. We've knocked them silly.

"I will tell you that I've had some very good talks with (Turkish) President (Recep Tayyip) Erdogan who wants to knock them out also and he'll do it. And others will do it too. Because we are in their region. They should be sharing the burden of costs and they're not," the US President said.

Last week, Trump surprised the world and his country as well when he suddenly announced that the US is pulling out its troops from Syria.

The US currently has some 2,000 troops in Syria, which are now gradually headed home. US Defence Secretary James Mattis resigned in protest.

Trump has argued that the US now no longer needs to be present in Syria now that ISIS has been defeated.

"We don't want to be taken advantage of any more by countries that use us and use our incredible military to protect them. They don't pay for it, and they're going to have to.

"In Syria, Erdogan said he wants to knock out ISIS, whatever's left, the remnants of ISIS. And Saudi Arabia just came out and said they are going to pay for some economic development. Which is great, that means we don't have to pay. We are spread out all over the world. We are in countries most people haven't even heard about. Frankly, it's ridiculous," Trump added.