In an ABC interview, William Barr said on Thursday that Trump’s behaviour was making it “impossible for me to do my job.”
Barr spoke after the Justice Department abandoned prosecutors’ initial recommendation to give the Stone seven to nine years in prison, prompting all four prosecutors to quit the case.
Trump has been weighing in on the matter on Twitter all week.
“I’m not going to be bullied or influenced by anybody ... whether it’s Congress, a newspaper editorial board or the president,” Barr said.
“I cannot do my job here at the department with a constant background commentary that undercuts me,” Barr said, adding: “I think it’s time to stop the tweeting about Department of Justice criminal cases.”
The White House said Trump was not concerned by Barr’s remarks.
“The president has full faith and confidence in Attorney General Barr to do his job and uphold the law,” White House spokeswoman Stephanie Grisham said in a statement.
Trump’s fellow Republicans also expressed support for Barr.
Senate Majority Leader Mitch McConnell, a staunch Trump supporter, said Barr was “a great choice” as attorney general.
“I think if the attorney general says it’s getting in the way of doing his job, maybe the president should listen to the attorney general,” McConnell told Fox News.
Stone was found guilty in November on seven counts of lying to Congress, obstruction and witness tampering.
Trump posted a Fox News story on Thursday that accused some of the jurors of political bias. “This is not looking good for the ‘Justice’ Department,” he tweeted.
Seth Cousins, who served as a juror in Stone’s trial, told Reuters he was “appalled” by Trump’s remarks.
“It feels like something outrageous is going on,” Cousins said in an interview.
“I think it is appalling for the president of the United States to be attacking American citizens for patriotically fulfilling their duties,” he said.
The Twitter attacks started on Tuesday when Trump criticised US prosecutors in the case stemming from former Special Counsel Robert Mueller’s investigation of Russian interference in the 2016 election to benefit Trump’s candidacy.
The Republican president called their sentencing recommendation for Stone “horrible” and a “miscarriage of justice.” Stone’s friendship with Trump dates back decades.
Trump on Wednesday thanked Barr, whom he appointed last year, for “taking charge” of the case. He also tweeted criticism of US District Judge Amy Berman Jackson, who is scheduled to sentence Stone on 20 February.
Trump and the Justice Department said they had not had direct talks on the matter.
House of Representatives Speaker Nancy Pelosi said Trump’s comments on the Stone case amounted to interference in the workings of the US government’s judicial branch.
“This is an abuse of power - that the president is again trying to manipulate federal law enforcement to serve his political interest,” Pelosi, a Democrat, told a news conference. “This is not what America is about. It is so wrong.”
Chief Judge Beryl Howell, the top judge on the US District Court in Washington on which Jackson sits, also weighed in, saying in an unusual public statement that public criticism “is not a factor” in sentencing decisions.