WASHINGTON (AFP) - US Attorney-General William Barr has agreed to testify to Congress amid allegations he has bent Justice Department policies to help President Donald Trump politically, the House Judiciary Committee announced Wednesday (Feb 12).

After refusing to appear for a year, Mr Barr will testify on March 31, the committee said in a letter to the Justice chief confirming the plan.

The letter, signed by committee chair Jerry Nadler and several Democratic members of the panel, said they have deep concerns about Mr Barr's conduct in legal matters involving the president.

"Since President Trump took office, we have repeatedly warned you and your predecessors that the misuse of our criminal justice system for political purposes is both dangerous to our democracy and unacceptable to the House Judiciary Committee," they said.

They cited acts from "the past week alone" that included Mr Barr's decision - allegedly under pressure from Mr Trump - to overrule his own prosecutors and seek a lighter prison sentence for veteran Republican political consultant Roger Stone, who has been convicted of lying to Congress and witness tampering.

That led to the resignation Tuesday of four Justice Department prosecutors from the case in apparent protest against political interference.

The letter also cited Mr Barr's revelation that he has opened a channel in the department to collect information for investigations involving Ukraine, the country at the centre of the recent impeachment trial, which ended in Mr Trump's acquittal by the Senate.

The committee also questioned the recent removal of the top federal prosecutor for Washington, Ms Jessie Liu. Ms Liu oversaw the prosecution of Mr Stone as well as two other former top Trump aides: 2016 campaign chair Paul Manafort and former White House national security advisor Michael Flynn.

Mr Barr has not spoken publicly about any of those issues, which have plunged the department into turmoil.

Mr Trump denied Wednesday that his tweets attacking the original stiff sentence of 87 to 108 months recommended for Stone, and in support of Mr Barr after it was reduced by more than half, amounted to political interference.

"They treated Roger Stone very badly," he added of his longtime political advisor.

Asked if he would pardon Stone, Mr Trump replied: "I don't want to say that yet."