Former FBI deputy director Andrew McCabe said US Deputy Attorney General Rod Rosenstein was "absolutely" supportive of the decision to investigate whether President Donald Trump was inappropriately aligned with Russia or whether he had obstructed justice.
Mr McCabe also told the 60 Minutes news programme that the FBI had good reason to investigate whether Mr Trump was in league with Russia following the May 2017 firing of FBI director James Comey.
He cited what he said were Mr Trump's efforts to publicly undermine the investigation into potential co-ordination between the Trump campaign and the Kremlin.
A US Justice Department spokeswoman declined to comment on Sunday night.
In excerpts released last week by CBS News, Mr McCabe also described a conversation about invoking the US constitution to remove Mr Trump from office.