FBI's Andrew McCabe stepping down after Trump accuses him of being partial

The FBI's deputy director, Andrew McCabe, is stepping down after having been accused by President Donald Trump of being a Democratic partisan, a government source confirmed on Tuesday.

McCabe is stopping work immediately but will remain on the FBI payroll until March to obtain retirement benefits, the source confirmed.

McCabe, 49, was expected to leave sometime early this year when he became fully eligible for a pension, after two decades in the bureau.

Trump targeted McCabe with critical tweets after it emerged that his wife had received a campaign contribution for a race in Virginia in 2015 from an ally of Trump rival Hillary Clinton.

McCabe and fired FBI director James Comey had key roles in the FBI's probe of Clinton in the 2016 election, which ultimately cleared the Democrat of criminal wrongdoing in her misuse of a personal email server while she was secretary of state.

Both were also involved in the initial stages of an ongoing investigation into whether the Trump campaign colluded with Russians during the election.

Trump has repeatedly dismissed collusion allegations as "fake news" and has accused the FBI of bias for pursuing the probe, now in the hands of special prosecutor Robert Mueller -- himself a former FBI director.