The Kremlin dismissed the reports as "complete nonsense".
The latest reports that Trump apparently leaked classified intelligence come just as the Capitol Hill was already grappling with the fallout from Trump's decision to fire FBI Director James Comey, who was investigating any possible ties between the Trump campaign and Russian Federation.
The Post report says that senior White House officials called the Central Intelligence Agency and NSA to alert them to Trump's disclosure.
At the White House, Mr Trump tweeted: "I wanted to share with Russian Federation (at an openly scheduled W.H. meeting) which I have the absolute right to do, facts pertaining.to terrorism and airline flight safety".
Without authorization from our ally, Trump revealed information to Russian Federation that would unmask undercover intelligence assets, hurting the ongoing fight against the vicious ISIS terror network.
In a meeting with Russian Foreign Minister Sergey Lavrov and Russian Ambassador Sergey Kislyak, Trump disclosed intelligence about a planned Daesh (ISIS) operation, which was supplied by a US ally, two officials with knowledge of the situation said. But the classified information he shared with a geopolitical foe was nonetheless explosive, having been provided by a critical US partner through an intelligence-sharing arrangement considered so delicate that some details were withheld even from top allies and other government officials.More news: Senators chase Fleury, rout Penguins in Game 3
The Obama officials said the Trump national security transition team did not follow protocol. The official spoke only on condition that neither he nor his country be identified, because he was not authorized to discuss the matter publicly. The Washington Post first reported the disclosure.
But some of the European partners Trump will meet later in his trip have been more skeptical about his policies, including a controversial travel and immigration ban that's been blocked by USA courts.
Citing a memo written by Mr Comey on a meeting with Mr Trump in the Oval Office, the report claims Mr Trump told the Federal Bureau of Investigation chief Mr Flynn had done nothing wrong. Several members of Congress said that if Trump did suggest that Comey "let this go" regarding Flynn's Russian contacts, it was probably just a joke, light banter.
Former FBI Director James Comey called Clinton and her State Department advisers "extremely careless" in their handling of classified information, but he did not recommend pursuing criminal charges.
It was, perhaps, even more remarkable that Trump chose to confide in representatives of an adversary, who could use the information to find its source.
New Jersey lawmakers expressed concern over a report in the Washington Post that President Trump divulged highly classified information about ISIS to the Russian foreign minister and ambassador last week at a meeting in the Oval Office.More news: Edouard named as French premier
National Security Adviser H.R. McMaster on Tuesday afternoon defended Trump's comments during last week's meeting, which he described as "wholly appropriate". The former US officials requested anonymity in order to discuss the handling of classified information.
"Israel has full confidence in our intelligence sharing relationship with the United States and looks forward to deepening that relationship in the years ahead under President Trump", Dermer said.
And, of course, there's the intelligence failures on a lack of weapons of mass destruction in Iraq, the rationale that led to the invasion of the country.
The NSA was also at the heart of the Edward Snowden drama, which revealed the U.S.to be spying on world leaders, including close allies. If Trump did nothing wrong, the White House could clear this up by releasing the transcript. The catch is that the law defines classified information as information determined classified by a USA government agency, and similarly defines an unauthorized person as someone not determined authorized by the executive branch.
Speaking to NPR's Morning Edition Tuesday, Coons called the allegations careless and risky.
The revelation also prompted cries of hypocrisy. Put another way, classified information becomes unclassified by default the moment the president chooses to disclose it.More news: UN court orders Pakistan not to execute Indian 'spy' Kulbhushan Jadhav
Chrystia Freeland and Harjit Sajjan dined with their USA counterparts for foreign affairs and defence - Rex Tillerson and James Mattis. The nature of specific threats was discussed, he said, but not sources, methods or military operations. Spicer will appear later, off-camera, to speak with White House reporters at 2 p.m. ET.
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