The main cast members of Guardians of the Galaxy have issued an open letter in support of ousted director James Gunn, who was fired earlier this month after jokes he made on Twitter years ago were uncovered.

Chris Pratt, Zoe Saldana, Bradley Cooper and six other cast members said they were not defending Gunn's jokes about rape and paedophilia, but wished to speak about his upstanding character on set and denounce what they see as a politically motivated "character assassination".

The Walt Disney Company fired Gunn from directing the third instalment 10 days ago after the tweets, which Gunn later deleted, were shared by alt-right agitator Mike Cernovich, who is known for promoting conspiracy theories like Pizzagate.

"We fully support James Gunn," the letter, which is also signed by cast members Dave Bautista, Karen Gillan, Sean Gunn, Vin Diesel, Pom Klementieff and Michael Rooker, says.

"We were all shocked by his abrupt firing last week and have intentionally waited these 10 days to respond in order to think, pray, listen and discuss."

Gunn said he accepted Disney's decision and apologised for "the way I conducted myself". ( Reuters: Hannah McKay )

The signatories said they were not trying to defend Gunn's comments, but to share their experience of having worked with him on the first two instalments of the series.

"The character he has shown in the wake of his firing is consistent with the man he was every day on set, and his apology, now and from years ago when first addressing these remarks, we believe is from the heart, a heart we all know, trust and love," they said.

Cernovich had kicked off the original outrage, sharing Gunn's old tweets and writing that they were "everything wrong with Hollywood".

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Days later the director was fired, with Walt Disney Studios chairman Alan Horn saying the tweets were "indefensible and inconsistent with our studio's values".

Gunn subsequently apologised for the comments and denied having ever engaged in the behaviour mentioned in the tweets.

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"My words of nearly a decade ago were, at the time, totally failed and unfortunate efforts to be provocative," Gunn said in a statement.

"I have regretted them for many years since — not just because they were stupid, not at all funny, wildly insensitive, and certainly not provocative like I had hoped, but also because they don't reflect the person I am today or have been for some time."

The cast members who signed the letter appeared to call out Cernovich for his role in what they called a "character assassination".

Gunn's current Twitter account is heavy on left-leaning politics, and he frequently spars with right-wing personalities.

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"There is little due process in the court of public opinion," they wrote.

"James is likely not the last good person to be put on trial.

"Given the growing political divide in this country, it's safe to say instances like this will continue, although we hope Americans from across the political spectrum can ease up on the character assassinations and stop weaponising mob mentality."

Gunn has been writer and director of the Guardians of the Galaxy franchise from the start, taking an obscure Marvel Comics title about a group of multicoloured misfits and turning it into a space opera decked with comedy and retro music that made Pratt a major movie star.

Through two instalments the franchise has brought in more than $1.5 billion in global box office.

The cast say they look forward to working with Gunn in the future.

The controversy comes in the wake of the high-profile cancelling of Roseanne after its star Roseanne Barr tweeted racist comments about a former Obama adviser.

After the Gunn story broke, Star Wars: The Last Jedi director Rian Johnson said he went through his timeline and deleted 20,000 old tweets out of caution.

"If trolls scrutinising it for ammunition is the new normal, this seems like a 'why not' move."

ABC/AP