Washington: The embattled FBI agent who oversaw the opening of the Russia investigation mounted an aggressive personal defence on Thursday, rejecting accusations that he let his private political views bias his official actions and labelling Republican preoccupation with him "another victory notch in Putin's belt."

"Let me be clear, unequivocally and under oath: not once in my 26 years of defending my nation did my personal opinions impact any official action I took," Peter Strzok, told House lawmakers investigating what Republicans say is evidence of rampant bias at the top levels of the FBI.

But in defending himself and his agency, Strzok had to weather hours of attacks by Republicans, whose accusations drifted from personal animus toward President Donald Trump to blatant lying and moral misconduct with a senior FBI lawyer, Lisa Page.

In his first public comments since private text messages between Strzok and Page were disclosed, the agent concluded opening remarks with a pointed broadside against his antagonisers.