New questions are being asked this morning, including by President Donald Trump, about who leaked the contents of former national security adviser Michael Flynn's phone calls with the Russian ambassador.

The real story here is why are there so many illegal leaks coming out of Washington? Will these leaks be happening as I deal on N.Korea etc? — Donald J. Trump (@realDonaldTrump) February 14, 2017

Flynn resigned late Monday, just days after the leaks led to reports that he had discussed the Obama administration's recent sanctions against Moscow with Amb. Sergey Kislyak.

Vice President Mike Pence and Press Secretary Sean Spicer had previously maintained that the sanctions were not discussed, based on denials from Flynn.

In a statement last night, Flynn said he "inadvertently briefed the Vice President Elect and others with incomplete information" about the calls.

Fox News chief intelligence correspondent Catherine Herridge reported this morning on new calls from Republicans for an investigation into the leaks and the surveillance of Flynn's calls by the intelligence community.

Herridge said that identifying the American caller for surveillance purposes, in this case Flynn, "needs sign-off at the highest levels."

House Intelligence Committee chairman Devin Nunes (R-CA) said authorization would have been needed to unmask Flynn's name.

"If in fact the press reports are right, someone made the decision to deliberately listen to General Flynn's phone calls," said Nunes, calling it "unprecedented, unwarranted and flat-out wrong."

Nunes said he will ask the FBI for an assessment of the recent leaks.

Watch the report above and the interview with Rep. Nunes below.

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