Michael Flynn, the retired general who was an early Donald Trump supporter, has resigned as National Security Adviser, Spectrum Networks has confirmed.

  • National Security Adviser Michael Flynn resigns
  • Flynn admits to not giving "complete information" about phone calls with Russia ambassador
  • Gen. Keith Kellogg acting adviser

Flynn's resignation comes amid growing reports confirming Flynn's alleged ties and communications with Russian officials leading up the president's inauguration.

The newest report in the Washington Post said the Justice Dept. had warned the Trump administration last month that Flynn misled administration officials about his communications with the Russian ambassador to the United States. 

The Justice Dept. even said Flynn was vulnerable to blackmail by the Russians.

Flynn was also unable to refute a Washington Post report last week that he talked with the Russian ambassador about recent sanctions imposed on Russia by the Obama administration about the country's meddling in the 2016 election.

The report said Flynn seemed to imply to Russian ambassador that sanctions against Russia would be eased. This conversation took place before the president's inauguration.

In his resignation letter, Flynn admitted he did not give complete information about his phone calls with the Russian ambassador.

Flynn said he was honored to serve with the president, who had "reoriented American foreign policy in fundamental ways to restore America's leadership position in the world" in just three weeks.

"In the course of my duties as the incoming National Security Advisor, I held numerous phone calls with foreign counterparts, ministers, and ambassadors. These calls were to facilitate a smooth transition and begin to build the necessary relationships between the President, his advisors and foreign leaders. Such calls are standard practice in any transition of this magnitude.

"Unfortunately, because of the fast pace of events, I inadvertently briefed the Vice President Elect and others with incomplete information regarding my phone calls with the Russian Ambassador. I have sincerely apologized to the President and the Vice President, and they have accepted my apology."

The discussion with the Russian ambassador was a brief of protocol, and some experts say it was possibly illegal.

Reports over the last month show several intelligence agencies were investigating Flynn, including the FBI and the Army.

Flynn was already a controversial figure in Trump's inner circle when he was named National Security Adviser. 

He was Defense Intelligence Agency director under the Obama administration from 2011 to 2014. Reportedly, Flynn was forced out of the DIA because he clashed with superiors over his management style. 

Flynn accused the Obama administration of not wanting to hear the truth about Syria and ISIS. 

He was also chided during the 2016 election for posting links to fake news on his Twitter account.

Gen. Keith Kellogg has been named acting National Security Adviser. Also on the short list is retired General David Petraeus.

Information from AP and CNN were used in this report.