Donald Trump has promised to send all Syrian refugees back home if he becomes president.

In a speech in New Hampshire yesterday, he warned that Syrian asylum seekers could be a fifth column sent by Islamic State.

"If I win, they're going back" said the billionaire, who is currently frontrunner in the race to become the Republican presidential candidate.

He expressed outrage that the US would want to take in 200,000 Syrian refugees – a policy reversal from earlier this month when he told Fox News that the US should take in more refugees on a "humanitarian basis."

"I hate the concept of it, but on a humanitarian basis, with what's happening, you have to," he said on 8 September when asked whether Syrian migrants should be allowed in to the US.

However his comments yesterday were more in line with Trump's typical hard-line migration policy.

"I hear we want to take in 200,000 Syrians. And they could be – listen, they could be ISIS," he told the Republican rally.

"I'm putting the people on notice that are coming here from Syria as part of this mass migration, that if I win, if I win, they're going back."

Trump has previously said the refugee crisis in the Middle East "could be one of the greatest tactical ploys of all time."

His speech in New Hampshire was notably different to what fellow candidate, Jeb Bush, said at a simultaneous event.

"I think we're duty bound to provide support," Bush told his rally, which was considerably smaller than Trump's.

"This is normally what we do unbelievably well. We act on our heart, we organise it well, we take care of people. This is typically with support of government, but it's normally with organisations that do great work."

Since the Syrian conflict began four years ago, the US has accepted 1,500 Syrian refugees and the US government have pledged to take in 10,000 next year.

A number of Democrats, including Hillary Clinton, have urged the US to increase the number of Syrians from 10,000 to 65,000.

US Secretary of State John Kerry has pledged to take more refugees worldwide, raising the yearly cap from 70,000 to 85,000 next year and to 100,000 in 2017.

Half a million refugees have crossed the Mediterranean into Europe in 2015 alone.