Barack Obama and Donald Trump
President Barack Obama speaks while meeting with President-elect Donald Trump (L) following a meeting in the Oval Office November 10, 2016 in Washington, DC Win McNamee/Getty Images

Former President Barack Obama warned Donald Trump against hiring Michael Flynn as his National Security Advisor while Trump was President-elect, ex-Obama officials confirmed to CNN on 8 May.

Flynn was unceremoniously asked to resign from the administration after undisclosed phone calls with the Russian ambassador during which he is alleged to have spoken about dropping sanctions before he had taken public office.

The debacle also caused headaches for Vice President Mike Pence, who publicly defending Flynn – after reportedly not having been briefed on the full story.

The warning from Obama came during a meeting between the two presidents soon after Trump had been elected, the Associated Press reported.

Though allegedly warned about Flynn's contacts with the Russian ambassador, Trump still picked him to be his National Security Adviser – a post Flynn lasted less than a month in.

The disclosure also comes the same day that former acting-Attorney General Sally Yates is due to testify at a Senate Judiciary subcommittee hearing which is investigating Russian interference in the 2016 election.

Yates is expected to publicly acknowledge – on 8 May that she warned Trump officials about Flynn's 'connections' before the news hit the headlines.

The hearing seems to have Trump rattled. On the morning of 8 May, he fired off a series of tweets pointing the finger at the Obama administration, attempting to push the agenda onto the subject of leaks, rather than Flynn's connections.

Michael Flynn requests immunity in Trump-Russia investigation IBTimes US

"General Flynn was given the highest security clearance by the Obama Administration – but the Fake News seldom likes talking about that." Trump tweeted, referencing Flynn's former position as director of the Defense Intelligence Agency under Obama, a position he was reportedly fired from after accusations of erratic management.

Trump then went on to say: "Ask Sally Yates, under oath, if she knows how classified information got into the newspapers soon after she explained it to W.H. Counsel."

Yates was acting-Attorney General for the first 10 days of the Trump administration but was fired after directing Justice Department lawyers not to defend the first, and ultimately failed, travel ban.