Republican presidential hopeful Donald Trump promised Monday to turn the page on US foreign policy from nation-building to instead focus on destroying Islamic State.

"If I become president, the era of nation-building will be brought to a swift and decisive end," he said in a foreign policy speech in Youngstown, Ohio.

Trump blamed President Barack Obama and his would-be Democratic successor, Hillary Clinton, for allowing radical Islam to take root in the Middle East, pointing to Obama's withdrawal from Iraq and US military intervention in Libya.

Trump outlined a series of attacks by Islamic State and its sympathizers in the United States and Europe and accused Obama of failing to properly identify the enemy as "radical Islamic terrorists."

"We cannot always choose our friends, but we can never fail to recognize our enemies," Trump said.

He called for greater international cooperation in fighting terrorism, enhanced efforts to fight terrorist ideology online and greater screening of would-be immigrants and refugees from regions with widespread terrorist threats.

He praised the NATO alliance for taking a greater role in the fight against Islamic State, after the candidate previously questioned the role of the North Atlantic alliance and suggested the US could reconsider its role in the group.

Trump claimed to have strongly opposed George W Bush's 2003 invasion of Iraq - though there is no public record of him taking such a position - and said the US should have kept troops there to seize Iraqi oil reserves.

He criticized Obama's plans to increase the number of Syrian refugees admitted to the country and called for "extreme vetting" of potential refugees.

"We will have to temporarily suspend immigration from some of the most dangerous and volatile regions of the world that have a history of exporting terrorism," Trump said.

He took to task German Chancellor Angela Merkel for her refugee policy welcoming a flood of asylum seekers from Syria, Iraq and elsewhere.

"Hillary Clinton wants to be America's Angela Merkel - and you know what a disaster this massive immigration has been to Germany and the people of Germany," he said.

The speech echoed concerns of US voters amid a slew of terrorist attacks in the West in recent months and worries that potential terrorists could exploit the refugee process to enter the United States.

Only 36 per cent of Americans support taking in Syrian refugees, and the figure is even lower among Republicans, with just 18 per cent in favour, according to a survey by the Chicago Council on Global Affairs, released Monday.

Trump's remarks come amid increased scrutiny of his campaign and his off-the-cuff, inflammatory statements.

The conservative-leaning Wall Street Journal editorial board on Monday called on Trump to change his ways and campaign with more discipline - or step aside in favour of his vice presidential running mate, Indiana Governor Mike Pence.

"If they can't get Mr Trump to change his act by Labour Day [September 5], the GOP will have no choice but to write off the nominee as hopeless and focus on salvaging the Senate and House and other down-ballot races," they wrote.

On Monday, Trump stuck largely to prepared remarks and read his speech from a teleprompter, something he does rarely.

The campaign continued to come under fire, as The New York Times detailed Trump campaign chairman Paul Manafort's work for ousted Ukrainian president Viktor Yanukovych. Manafort was paid 12.7 million dollars by the pro-Russian politician over six years.

Clinton's campaign warned that Trump was "unfit to be our commander in chief." While Vice President Joe Biden, campaigning with Clinton in Pennsylvania said he was headed abroad this month to reassure US allies who are increasingly concerned by Trump's isolationist rhetoric.

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