Russian officials developed a relationship with Michael Flynn over the course of months and bragged that they could use him to influence Donald Trump, sources said.

'This was a five-alarm fire from early on, the way the Russians were talking about him,' a former Obama administration official told CNN.

Flynn was caught speaking to Russian ambassador Sergey Kislyak in a December phone call that eventually led to his forced resignation just 24 days into his role as National Security Adviser.

After Barack Obama hit back at Russia for meddling in the elections, Flynn told Kislyak the Trump administration would approve of Russia's decision to hold off on retaliating, sources said.

Flynn went on to say the Trump administration would revisit the sanctions imposed since Russia annexed Crimea in 2014, the sources said, and Putin followed his advice, announcing the next day that he would not retaliate.

Russian officials viewed Michael Flynn as an ally and bragged that they could use him to influence Donald Trump, sources told CNN

Flynn (right) developed a relationship with Russian officials for several months in 2016 before he was caught speaking to Russian ambassador Sergey Kislyak in a December, sources said

The Russians saw Flynn as an ally, and while officials expressed their concerns, they also raised the possibility that the Russians may have exaggerated their clout on Trump's inner circle.

An official from the former administration also told CNN Flynn was viewed as a potential national security problem, echoing Sally Yates' testimony that Flynn could be subject to blackmail by the Russians.

And Barack Obama warned Trump against hiring Flynn during a face-to-face meeting back in November,CNN reported earlier this month.

But a White House Official issued a statement that read: 'We are confident that when these inquiries are complete there will be no evidence to support any collusion between the campaign and Russia.

'This matter is not going to distract the President or this administration from its work to bring back jobs and keep America safe.'

While Flynn's time in the White House was brief, he is still under investigation by the Senate Judiciary Committee and House Oversight and Government Reform Committee.

Flynn reportedly told Trump's chief lawyer Donald McGahn on January 4 that he was under investigation for secretly working as a paid lobbyist for Turkey during the campaign.

Flynn's discussions of US sanctions with Kislyak (above) eventually led to his forced resignation just 24 days into his role as National Security Adviser

Flynn admitted that his lobbying firm was paid $530,000 for work that could have benefited the Turkish government just two months before he was appointed to the White House.

Flynn's consulting firm, Flynn Intel Group, was lobbying for a Dutch consulting firm with ties to Turkish President Recep Tayyip Erdogan before and immediately after the US election.

He failed to file documents with the Justice Department declaring he was a foreign agent until March, weeks after he resigned.

In the documents, he said the lobbying work 'could be construed to have principally benefited the Republic of Turkey.'

Flynn admitted that his lobbying firm was paid $530,000 for work that could have benefited Turkey (pictured Turkish President Tayyip Erdogan)

The filing also disclosed that Flynn secretly met with the Turkish foreign and energy ministers in New York before Election Day.

Flynn wrote an op-ed the day Trump was elected calling for the US to kick out anti-government Turkish cleric, Fethullah Gulen, who is living in exile in Pennsylvania.

Flynn also blocked a military plan against the Islamic State group that was opposed by Turkey.

After Flynn was forced to resign, Trump reportedly tried to get former FBI Director James Comey to drop the investigation into the ex-general.

Comey did not. He was controversially fired by the president on May 9.