The US attorney general has been accused of “waging a media campaign” for President Donald Trump ahead of the Mueller report’s long-awaited release.
Democrat Jerry Nadler accused William Barr of failing to let “the facts speak for themselves” over his plans to hold a news conference before the release.
The 400-page report is the result of an investigation into alleged Russian interference during the 2016 election.
A summary, released by Mr Barr, reveals it clears Mr Trump of any collusion.
However, it does not go as far as to completely exonerate the president of obstruction of justice.
Both Mr Trump’s supporters and detractors are now eagerly awaiting the full – albeit redacted – report’s release.
It will be sent to Congress between 11:00 and midday local time (15:00 GMT and 16:00 GMT). It will be published online sometime after this.
Mr Barr is due to hold a news conference at 09:30.
The report contains the findings of a 22-month investigation into possible collusion between Russia and the Trump presidential campaign back in 2016.
It was led by Special Counsel Robert Mueller, who was chosen to run the investigation in 2017 following concerns from US intelligence agencies that Russia had tried to tip the election in Mr Trump’s favour.
