Donald Trump has said that he would implement "extreme vetting" of immigrants and suspend immigration from certain countries to protect the United States.
The Republican candidate for the US Presidential election was giving his foreign policy speech in Ohio.
Mr Trump also vowed to "crush and destroy" the so-called Islamic State group, accusing his Democratic rival Hillary Clinton and President Barack Obama of allowing it to grow.
He said that he would work closely with NATO allies to defeat the militant group if he won the election, reversing an earlier threat that the US might not meet its NATO treaty obligations with allies.
His remarks about NATO earlier this summer drew heavy criticism from allies.
He also pledged to launch a "commission on radical Islam" to root out jihadist networks and stop radicalization of young Americans.
"We should only admit into this country those who share our values and respect our people," he said.
"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."
Mr Trump called for a "new approach" to fighting terror, slamming the policies put in place by Mr Obama and Mrs Clinton, who served as his first secretary of state.
"Our current strategy of nation building and regime change is a proven absolute failure. We have created the vacuums that allow terrorism to grow and thrive," he said.
Mr Trump said he would suspend immigration from "some of the most dangerous and volatile regions of the world, that have a history of exporting terrorism."
Earlier, Mr Trump sharply criticised media outlets following news reports that he has grown depressed and sullen over his fading presidential prospects.
"I am not running against Crooked Hillary Clinton," the presidential candidate said in a speech in Fairfield, Connecticut. "I'm running against the crooked media."
Mr Trump seemed particularly upset with a New York Times article that quotes unnamed associates of his as saying that in private "his mood is often sullen and erratic."
Republicans close to his campaign were quoted as saying he was "exhausted, frustrated and still bewildered" by the political process.
The real estate tycoon returned to his message yesterday, tweeting: "My rallies are not covered properly by the media. They never discuss the real message and never show crowd size or enthusiasm."
Later, amid a flurry of further tweets on the subject, he added: "It is not 'freedom of the press' when newspapers and others are allowed to say and write whatever they want even if it is completely false!"
He has stripped a long list of news organisations - including the New York Times, Buzzfeed, Politico and the Washington Post - of their credentials, and vowed that as president he would make it easier to sue news outlets.
But media monitors say he has received more extensive coverage than any candidate in years.
A prominent US journalist, James Fallows of The Atlantic magazine, suggested Mr Trump's very criticism reflected a degree of desperation, tweeting: "I've seen winning campaigns and losing ones. 100% Iron Law: campaign saying 'our problem is the media' is campaign on way down."
But Paul Manafort, the Trump campaign chairman, pushed back against that notion during an appearance on CNN, saying, "The campaign is moving forward and very strong. We raised over $132m in the last two months."
I am not only fighting Crooked Hillary, I am fighting the dishonest and corrupt media and her government protection process. People get it!
— Donald J. Trump (@realDonaldTrump) August 14, 2016
It is not "freedom of the press" when newspapers and others are allowed to say and write whatever they want even if it is completely false!
— Donald J. Trump (@realDonaldTrump) August 14, 2016
I have always been the same person-remain true to self.The media wants me to change but it would be very dishonest to supporters to do so!
— Donald J. Trump (@realDonaldTrump) August 14, 2016
He noted that Mr Trump had visited key battleground states such as Pennsylvania, Ohio and Florida repeatedly and was "starting to get traction in those states."
However, recent polls have shown Mr Trump's numbers sagging badly in those states, notably hurt by his critical comments about the Muslim parents of a fallen US soldier, and what some saw as his suggestion that "Second Amendment people" - gun lovers - take their dislike for Hillary Clinton into their own hands.
Mr Manafort repeated the Trump claim that his Second Amendment remark was meant purely as an exhortation to vote.
But even one of Mr Trump's top advisors, Senator Jeff Sessions of Alabama, conceded that the candidate needed to communicate "more effectively."
