President Donald Trump's attorney general nominee, William Barr, has said he will allow special counsel Robert Mueller to finish the investigation into Russia's role in the 2016 presidential election, Republican Sen. Lindsey Graham said on Wednesday.

Graham told reporters Barr assured him the investigation would continue. "I can assure you he has a very high opinion of Mr. Mueller and he is committed to letting Mr. Mueller finish his job," Graham said.

The U.S. Senate Judiciary Committee will hold confirmation hearings on Jan. 15 and 16 for Barr, who has come under fire from Democrats for his criticism of the special counsel's Russia probe.

Senate Democratic leader Chuck Schumer said last month that a memo Barr wrote criticizing Mueller's investigation into possible Russian interference in U.S. elections should disqualify him from serving as attorney general.

Deputy U.S. Attorney General Rod Rosenstein, who has overseen the Russian election meddling probe, is preparing to leave the U.S. Department of Justice in coming weeks as President Donald Trump's nominee to lead the department is set to take over, a department official said on Wednesday.