She made the remarks after a two-day Washington visit where she met numerous lawmakers and administration officials - one of them being the newly sworn in USA trade czar, Robert Lighthizer, who will play a role in the renegotiation of NAFTA.
Vice President Mike Pence insisted that national security adviser Mike Flynn had not discussed Obama-era Russian sanctions when he and Kislyak spoke during Trump's transition to power.
Trump also reportedly boasted to the Russians about the intelligence he was receiving, telling the two men, "I get great intel". European allies have also privately expressed concern.
Trump has kicked up a cloud of ethics violations by refusing to enter into a blind trust, is under investigation for Russian collusion while repeatedly interfering with officials involved in the process, and has tried to distract from these issues by rolling out an unpopular health care repeal plan.
Today's pushback from Mr Trump comes after a Washington Post report, later confirmed by other media outlets, said he jeopardised a critical intelligence source by disclosing information that had been regarded as highly secret, even inside the U.S. government.
But the president admitted the basic details on Twitter - and he said it was no big deal.
"The question is simply a yes or no question here: Did the president share classified information with the Russians in that meeting?" Following a meeting with Turkish President Recep Tayyip Erdogan, Trump said only that his meeting last week with Russian Foreign Minister Sergey Lavrov was "very, very successful".
The latest drama has rattled already shaky confidence in the president in Washington. "This is not how a White House should operate", Schumer said.
"Russia is not a friend to the United States, and protecting our country's classified information from our adversaries is essential", he said in a statement provided to PhillyVoice by staff at Toomey's Washington, D.C. office.More news: Anti-Palestinian Jewish attorney arrives in Israel as new United States envoy
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Putin spoke at a time when in the US, talk of impeaching Trump has migrated from the fringes of political discourse to the mainstream, as NPR's Domenico Montanaro reports today.
The officials said the information had been supplied by a United States ally in the fight against the militant group.
"The partner had not given the United States permission to share the material with Russian Federation, and officials said Trump's decision to do so endangers cooperation from an ally that has access to the inner workings of the Islamic State".
Version Two: Trump weighed in Tuesday by indicating he had the authority to disclose whatever he'd like.
He did not dispute the accuracy of the details - as the administration appeared to do the previous day.
"I was in the room, the Secretary of State was in the room, as you know, the deputy adviser for national security, Dina Powell, and none of us felt in any way that conversation was inappropriate", McMaster was quoted as saying.
On rare occasions, presidents have revealed classified information when they have found it necessary to justify or explain their actions to the public, historian Timothy Naftali of New York University noted in a piece he wrote in January. The official questioned why - if Comey had concerns about his conversations with the president - the Federal Bureau of Investigation director hadn't shared them with the deputy director, the Department of Justice and Congress at the time.
A rare Democratic senator who's been friendly with Trump offered some advice: be more careful. "It's above top secret", King said.
Islamic State, or ISIS, holds territory in Iraq and Syria and is a common foe of Moscow and Washington.