"The Obama-Clinton foreign policy unleashed ISIS (and) de-stabilized the Middle East," Trump said in a foreign policy speech in the swing state of Ohio on Monday.

He criticized the Obama administration over the Syria policies, which he said are behind the spread of terrorism in the world.

"Our current strategy of nation building and regime change (in Syria) is a proven absolute failure. We have created the vacuums that allow terrorism to grow and thrive," he said.

Trump promised to "crush and destroy" ISIS, saying he "will work closely with NATO on this mission."

On his immigration policies, Trump said he would create a new screening test, which he called "extreme vetting."

"In the Cold War, we had an ideological screening test. The time is overdue to develop a new screening test for the threats we face today. I call it extreme vetting."

“A Trump administration will establish a clear principle that will govern all decisions pertaining to immigration and we will be tough and we will be even extreme,” he said, adding he would “only admit to this country those who share our values and respect our people.”

He also said that, under his administration, the State Department and the Department of Homeland Security would create a list of regions where the US would not admit people from.

Trump has been under criticism over his inflammatory remarks and policy proposals such as temporarily banning Muslims from entering the country and building a wall along the US-Mexican border.

He is in danger of losing his grip on the Republican Party, with fears growing that the New York businessman is heading for a “landslide defeat” to his rival Clinton in the November election.

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