In a major speech, Trump delivered a withering critique of Barack Obama`s foreign policy, saying the Democratic president has let China take advantage of the United States and has failed to defeat Islamic State militants. He pledged to "shake the rust off America`s foreign policy."

The New York billionaire spoke the day after victories in five Northeastern states that moved him closer to capturing the Republican Party presidential nomination for the Nov. 8 election.

With U.S.-Russian relations strained over numerous issues including Moscow`s support for Syrian President Bashar al-Assad, Trump said "an easing of tensions with Russia from a position of strength" is possible.

Trump, a real estate magnate, also said he would use U.S. economic leverage to persuade China to rein in North Korea`s nuclear program.

"China respects strength and by letting them take advantage of us economically we have lost all their respect," he said.

Trump said he would call separate summits of NATO and Asian allies to discuss a "rebalancing" of the U.S. financial commitment to their defense.

He was stern in charging that American allies have benefited from a U.S. defense umbrella but have not paid their fair share.

"The countries we defend must pay for the cost of this defense. If not, the U.S. must be prepared to let these countries defend themselves. We have no choice," Trump said.

Trump, a reality TV star, has never held elected office and has built support - particularly among white working class voters - with a no-nonsense style and populist pledges to "make America great again."

He set aside his rancorous campaign rhetoric for his address on foreign policy, delivered at a downtown Washington hotel.

Trump usually speaks in an off-the-cuff manner, but he delivered Wednesday`s speech with the aid of a teleprompter as he sought to make himself appealing to more Republican voters.

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