WASHINGTON (REUTERS) - The US Justice Department has launched an internal inquiry into circumstances surrounding the decision to ease sentencing recommendations for President Donald Trump's long-time friend Roger Stone, a spokesman confirmed.

"We welcome the review," Justice Department spokesman Kerri Kupec said.

The review by the department's inspector-general comes after Aaron Zelinsky, a career prosecutor, told lawmakers during a congressional hearing in June that his office received "heavy pressure from the highest levels of the Department of Justice"to ease its sentencing recommendation for Stone, a political ally of the president.

"Roger Stone was being treated differently from every other defendant. He received breaks that are, in my experience, unheard of," Zelinsky told the House Judiciary Committee during his testimony.

He and three other prosecutors withdrew from the case after senior department officials filed a new sentencing memo that backed away from the original recommendation of seven to nine years in prison.

Stone, 67, was convicted of obstruction, witness tampering and lying to Congress during its investigation into Russian interference in the 2016 presidential election.

In July, Trump commuted Stone's sentence and proclaimed that Stone had been targeted by "an illegal witch hunt."

The inspector-general's inquiry into Stone's sentencing was reported earlier on Monday by NBC News.

According to that report, the review was triggered by Zelinsky's testimony.

A spokesman for the Justice Department's Office of the Inspector-General said she can neither confirm nor deny the existence of an investigation.

Stone did not immediately respond to a request for comment on the news.