Greens MP Adam Bandt has apologised to new Liberal senator Jim Molan, for saying he could be a war criminal.

In a television interview earlier this week, Mr Bandt Senator Molan would "probably be up for prosecution" if there was an independent review into his actions in the Iraq War, when he was the chief of operations for the US-led coalition forces.

Senator Molan said he was considering legal action, but invited the Greens MP to "end the problem" by making a public apology.

Liberal Senator Jim Molan (AAP).

"I hereby apologise for those statements," Mr Bandt said in a statement this afternoon.

Senator Molan told 9NEWS Mr Bandt's comments were completely untrue.

"It goes to the reputation of the military. They cannot be left to stand," he said.

Adam Bandt, December 2017 (AAP).

Mr Bandt also called Senator Molan a "coward" for failing to speak out against the far-right group Britain First, after sharing two of its social media posts.

Senator Molan's posts also drew criticism from the widower of British Labour MP, Jo Cox, who was killed by a far right extremist.

Brendan Cox has told Fairfax Media that he believed Australians, like the British, would overwhelmingly reject Britain First and what it stands for.

Jim Molan, former Australian Army Major General.

"I believe the people of Australia, like the people here in the UK, will always choose hope over despair," Mr Cox said.