In an ill-tempered news conference at Trump Tower in Manhattan, the billionaire accused the media of failing to give him credit for raising the funds at an event in January in Iowa.
His tirade, in which he called one reporter "a sleaze" and another a "real beauty," overshadowed what otherwise should have been an upbeat event for the Republican.
"The press should be ashamed of themselves," he told reporters gathered before him. "You make me look very bad. I've never received such bad publicity for doing a good job."
While Trump has long had an adversarial relationship with the media, questions about the donations to veterans touched a raw nerve with him as he tries to build a conservative base ahead of the Nov. 8 general election.
Reporters have been persistently asking whether Trump in fact raised all the money he said he had in January and why it took so long to hand donations over to veterans groups.
A number of veterans groups listed by Trump on Tuesday as recipients confirmed they had received the donation as listed, ranging from $25,000 to, in one case, $1.1 million, which went to the Marine Corps Law Enforcement Foundation.
Some of the donations arrived in February or March, some as recently as last week. The money arrived in the form of a check from the Donald J. Trump Foundation.
"We received a $75,000 gift early last week from the Trump Foundation, it was not restricted or earmarked in any way," said Katherine Fritz, director of development at America's Vetdogs.
Trump's criticism of the media dashed the hopes of some Republican leaders who want him to tone down his rhetoric and become more magnanimous now that he has sealed the Republican presidential nomination.
The Washington Post said Trump only handed over a personal donation of $1 million last week - four months after announcing it - once the newspaper started asking about the money.
Trump said the coverage of his veterans group donations had been close to libelous. Asked whether he would keep his adversarial stance with reporters if elected president, Trump said: "Yeah, it's going to be like this."
A reporter told Trump he seemed resistant to the kind of scrutiny that comes with the office of US president.
But Ari Fleischer, a former White House press secretary for President George W. Bush, said the news media should stop fretting about how Trump treats them.
"My advice to the press: Stop interviewing yourselves about Trump's attack on the press. Don't worry about it. Just do your jobs and be fair," he said.
CLINTON POLL LEAD
The campaign of Democratic front-runner Hillary Clinton sought to take advantage of Trump's discomfort by holding a conference call with reporters to accuse him of hypocrisy over veterans' issues.
John Douglass, a retired Air Force general and Clinton backer, raised Trump's disparagement a year ago of U.S. Senator John McCain of Arizona, a war veteran. Trump had said McCain, a former Vietnam prisoner of war, was not a hero because he got captured.
"For him to disparage that service is despicable and disgraceful," Douglass said.
Clinton leads Trump by 11 percentage points in the latest Reuters/Ipsos poll. According to the May 27-31 survey of likely voters, 46 percent support the former US secretary of state while 35 percent back Trump.
California Governor Jerry Brown on Tuesday endorsed Clinton for the Democratic nomination, saying it was the only way to "stop the dangerous candidacy of Donald Trump."
The New York real estate mogul on Tuesday also bristled at the possibility that Republicans opposed to him might run a third-party candidate as an alternative to Trump or the expected Democratic nominee Clinton.
He said a leader of that effort, Bill Kristol, editor of the Weekly Standard magazine, "looks like such a fool."
"Let me tell you these people are losers," said Trump, adding that a third-party candidacy would guarantee Clinton wins the White House and deny Republicans the chance to put conservatives on the Supreme Court.
"What you're going to do is lose the election for the Republicans and therefore you lose the Supreme Court," he said.
Trump read out a list of veterans' organizations that had received money from the January event, which he attended instead of participating in a Fox News-sponsored candidates' debate. He said the money was benefiting 41 groups and that the total of cash raised could climb as more comes in.
He turned the microphone over briefly to Al Baldasaro, a Trump supporter and a veteran from New Hampshire who also skewered the news media, saying reporters should "get your head out of your butt, focus on the real issues."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)