Matt Hancock has said he knew Dominic Cummings wanted him to be fired as health secretary last year.
Appearing before MPs, Mr Hancock accused the PM's former aide of briefing journalists against him.
He also rejected a string of accusations levelled at him by Mr Cummings about his handling of the Covid pandemic.
He insisted he had always had the "wholehearted support" of Boris Johnson.
In his own appearance before MPs last month, Mr Cummings said he had repeatedly called on Mr Johnson to sack Mr Hancock.
Asked on Thursday whether he knew Mr Cummings had wanted him gone, Mr Hancock replied: "Yes, because he briefed the newspapers at the time."
He then added: "Somebody briefed the newspapers - I now have a better idea of who it was".
He said he had "no idea" why Mr Cummings appeared to have so much animosity towards him, but he took a swipe at Mr Johnson's former top aide, who left Downing Street in December after losing an internal power struggle.
"I think the best thing to say about this, and this will be corroborated by lots of people in government, the best thing to say, is that government has operated better in the past six months."
Mr Hancock also denied an accusation from Mr Cummings that he had blamed initial difficulties in buying protective equipment during the pandemic's first wave on Chancellor Rishi Sunak and NHS England chief Sir Simon Stevens.
Mr Hancock said this was "not a fair recollection of the situation," adding he had asked the chancellor to remove a price cap on buying kit, which Mr Sunak then "rapidly" agreed to do.
He said he could not "recall" whether Mark Sedwill, the UK's most senior civil servant at the time, launched an investigation into the matter - another claim by Mr Cummings.
The health secretary is giving evidence to the Commons health and science committees, as part of their joint inquiry into the government's handling of the pandemic.
The chair of the science committee, Greg Clark, said at the start of Thursday's session that they had asked Mr Cummings for documentary evidence to back up his allegations against Mr Hancock.
But he added that they had not yet received any, "nor any explanation" from Mr Cummings.