Trump took to Twitter to address reports that he passed ultra-sensitive classified information about the Islamic State group -- gleaned by a foreign intelligence partner -- to Kremlin emissaries.
The scandal has engulfed Trump's presidency and could corrode trust among allies who had been willing to share intelligence with the United States on the understanding it would be properly handled.
White House aides refused to say whether the information pertaining to the group's bomb-making capabilities was classified.
But the president insisted he had the "absolute right" to share "facts pertaining... to terrorism and airline flight safety" with Russia.
The Washington Post reported on Monday that Trump disclosed revealing details about the origin of the threat to Russian Foreign Minister Sergei Lavrov and Moscow's man in Washington Sergey Kislyak during a controversial meeting last week.
The New York Times reported that the information was provided, at least in part, by Israel -- which had allegedly urged Washington be careful in handling it.
In defending his disclosures to the Russian officials, Trump cited "humanitarian reasons" and an effort to get the Kremlin to "greatly step up" its fight against the Islamic State group.
"We had a very successful meeting with the foreign minister of Russia," Trump later said. "We're going to have a lot of great success over the next coming years and we want to get as many to help fight terrorism as possible."
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The president's National Security Adviser H.R. McMaster, who entered the administration after a stellar military career, was tasked with cleaning up a scandal that has further called the future of Trump's presidency into question.
McMaster denied the president had caused a "lapse in national security," saying it was "wholly appropriate for the president to share whatever information he thinks is necessary to advance the security of the American people."
McMaster also indicated that Trump could not have revealed sensitive sources or methods.
"The president wasn't even aware where this information came from," said McMaster. "He wasn't briefed on the source or method of the information either."
Kremlin spokesman Dmitry Peskov on Tuesday dubbed the news "nonsense," saying it was not worth confirming or denying.
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The Post, citing unnamed officials, said Trump went off script during the meeting, describing details about an Islamic State terror threat related to the use of laptop computers on airplanes, and revealing the city where the information was gathered.
The Trump administration recently barred the use of laptops in the passenger cabin from several countries in the Middle East and is mulling the expansion of that ban to cover jets originating in Europe.
The Post report sparked the latest in a wave of firestorms to engulf the White House, leaving aides frantically trying to douse the flames and determine the source of such damaging leaks.
"I have been asking Director Comey & others, from the beginning of my administration, to find the LEAKERS in the intelligence community," Trump tweeted Tuesday.
Since coming to office in January, Trump has lurched from crisis to crisis, lampooning the intelligence services, law enforcement and the media along the way.
Trump's meeting with top Russian diplomats last week came one day after he threw his administration into turmoil by taking the rare step of firing his FBI director James Comey.
Comey had been overseeing investigations into possible Trump campaign collusion with Russia to skew the 2016 election.
Ryan wants 'full explanation'
But political and legal experts said this latest misstep is among the most egregious so far of Trump's presidency.
For Trump's already weary allies in Congress, it brought more headaches and demanded yet more explanation from an administration that is struggling to leave its legislative mark.
"The White House has got to do something soon to bring itself under control and in order. It's got to happen," said Republican Senator Bob Corker.
"Obviously, they're in a downward spiral right now, and they've got to figure out a way to come to grips (with) all that's happening," Corker said.
Meanwhile, top Senate Democrat Chuck Schumer accused Trump of potentially putting American lives at risk.
"If the report is true, it is very disturbing. Revealing classified information at this level is extremely dangerous and puts at risk the lives of Americans and those who gather intelligence for our country," the New York senator said.
"The president owes the intelligence community, the American people and Congress a full explanation."
