Republican presidential front-runner Donald Trump said Wednesday the United States has lacked a coherent foreign policy since the end of the cold war and must "shake the rust off" its approach to foreign matters.

In his first major foreign policy address of the campaign, Trump said that "America first" would be the overriding theme of his administration. "I will view as president the world through the clear lens of American interests," said Trump, speaking in Washington one day after winning primaries held in five north-eastern US states.

Reading from a script, Trump was unsparing in his critique of the foreign policy of the President Barack Obama and former secretary of state Hillary Clinton, which he slammed as a "complete and total disaster" that left a legacy of "weakness, confusion and disarray."

Noting that he did not support the Iraq war, which cost thousands of US lives and trillions of dollars, Trump said that it led to the rise of Islamic State and emboldened Iran. If elected, Trump said the US would be "getting out of the nation-building business."

Trump also pointed to Libya, Egypt and Syria as other failures of recent US policy, and said the Middle East was "more unstable and chaotic than ever before."

Outside of the Middle East, Trump said that he would push allies to "contribute ... to our tremendous security burden," claiming that besides the US only four of the 28 NATO member countries devote the required 2-per cent of GDP towards their defence.

While noting that the US has "serious differences" with Russia and China, Trump said they didn't have to be adversaries.

Ending the "horrible cycle of hostility" with Russia would be mutually beneficial to both nations, Trump suggested, and an easing of tensions was possible from a position of strength.

"If we can't make a deal under my administration, a deal that's great - not good, great - for America, but also good for Russia, then we will quickly walk from the table. It's as simple as that. We're going to find out," Trump said.

He said that China wouldn't be establishing bases in the South China Sea if it had more respect for the US.

"China respects strength," Trump said, "and by letting them take advantage of us economically, which they are doing like never before, we have lost all of their respect."

The real estate mogul also revisited his controversial proposal to halt the flow of Muslim immigrants to the US, saying there were "scores of recent migrants inside our borders charged with terrorism."

"We have no idea where these people are coming from. There's no documentation," Trump alleged. "A pause for reassessment will help us to prevent the next San Bernardino or frankly, much worse," he said, referring to the December attack in California carried out by a radicalized married couple.

He also offered strong words for Islamic State: "I have a simple message for them. Their days are numbered. I won't tell them where and I won't tell them how."

Trump promised to rebuild the US military while rejecting the "false song of globalism" that led to trade agreements such as the North American Free Trade Agreement (NAFTA) between the US, Canada and Mexico, which he called a "total disaster" for the US economy.

"The world is most peaceful and most prosperous when America is strongest," Trump said.

He said that if the US regains its strength, wealth and respect, "perhaps this century can be the most peaceful and prosperous the world has ever, ever known."

White House spokesman Josh Earnest refuted Trump's claims, saying "there is no denying the United States is safer and stronger than we were when President Obama took office in January 2009."

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