US attorney general says Trump tweets 'make it impossible' to do job

US Attorney General Bill Barr has accused Donald Trump of hampering the work of the Justice Department, saying the president's tweets were making his job "impossible".

"I have a problem with some of the tweets," Barr said in an interview with ABC News, adding: "I cannot do my job here at the department with a constant background commentary that undercuts me."

"I think it's time to stop the tweeting about Department of Justice criminal cases," he said.

Barr is due to testify to Congress next month amid allegations that he decided -- allegedly under pressure from Trump -- to overrule his own prosecutors and seek a lighter prison sentence for Republican political consultant Roger Stone.

Four Justice Department prosecutors resigned from the case this week in apparent protest against political interference from the president.

Trump has denied that his tweets attacking the original stiff sentence of 87 to 108 months recommended for Stone -- and in support of Barr after it was reduced by more than half -- amounted to political interference. When asked whether he had spoken with Trump about recommendations in the Stone case, Barr replied: "Never".

"I'm happy to say that in fact the president has never asked me to do anything in a criminal case."

Asked whether he was prepared for repercussions for speaking out against Trump, Barr replied: "Of course." "I'm not going to be bullied or influenced by anybody," he said, "whether it's Congress, newspaper editorial boards, or the president, I'm going to do what I think is right".