The Wagner chief said Wednesday that Russians should be allowed to criticise top military commanders, after lawmakers tightened penalties for discrediting forces fighting in Ukraine.

On Tuesday, parliament's lower house approved legislation introducing heavy jail terms for people who criticise mercenaries including members of the Wagner group, a measure that only applied to regular forces before.

Wagner chief Yevgeny Prigozhin said on Wednesday that people should feel free to express their opinion and only ordinary soldiers were beyond criticism.

"I think that the law against discrediting should not apply to the command staff, that is me, the minister of defence, and other leaders who make or can make mistakes during a special military operation," Prigozhin said on Telegram, referring to Moscow's assault on Ukraine.

"Society should say what it deems necessary about them," he said. "Only the soldier is sacred. So soldiers should be left alone."

Prigozhin -- an ally of President Vladimir Putin -- has for months been involved in a power struggle with the defence ministry, claiming battlefield victories ahead of Russia's army and accusing the military of not sharing ammunition with his forces.

Prigozhin also insisted he did not "discredit" anyone.

"I only speak the truth," he said, adding that his statements were vetted by his lawyers.

"Of course, anyone can be imprisoned, and so can I," he added.

"But in that case we should not forget that 146 million Russians could also be jailed, which is a path to nowhere."

Sanctioned by Washington and Brussels, Prigozhin had for years operated in the shadows, but has been thrown into the limelight since the start of the offensive in Ukraine.

He has sought to present his forces, who have been spearheading offensives against cities in eastern Ukraine including Bakhmut, as more efficient than Russia's regular army.