Irish filmmaker John Carney has apologised for slamming Keira Knightley's acting, saying his comments were "petty, mean and hurtful."

The director has issued an apology on Twitter in a statement saying: "I'm ashamed of myself that I could say such things and I've been trying to account for what they say about me. In trying to pick holes in my work, I ended up blaming someone else.

"That's not only bad directing, that's shoddy behaviour that I am not in any way proud of. It's arrogant and disrespectful."

He continued: "Keira was nothing but professional and dedicated during that film and she contributed hugely to its success."

From a director who feels like a complete idiot. pic.twitter.com/vfO8m4U2Hl— John Carney (@jayceefactory) June 1, 2016

Carney said he wrote to Knightley offering a personal apology but also wanted to publicly apologise to the actress, her fans and anyone else he had offended. He concluded with: "It's not something I could ever justify, and will never repeat."

The filmmaker is referring to comments made during an interview with the UK's The Independent where he spoke about working with Knightley on the musical comic drama Begin Again.

"Keira has an entourage that follow her everywhere so it's very hard to get any real work done," he said. "And as much as I tried to make it work I think that she didn't quite come out as a guitar-playing singer-songwriter. I learned that I'll never make a film with supermodels again."

He added: "I don't want to rubbish Keira, but you know it's hard being a film actor and it requires a certain level of honesty and self-analysis that I don't think she's ready for yet and I certainly don't think she was ready for on that film."

Fans and former collaborators defended the actress, including Mark Romanek, who directed her in the thriller Never Let Me Go.

He took to Twitter to say: "My experience with #keiraknightley was utterly spectacular on every level. I have no clue what this guy is talking about."

My experience with #keiraknightley was utterly spectacular on every level. I have no clue what this guy is talking about. #arrogantshithead— mark romanek (@markromanek) May 30, 2016

My recollection of #keiraknightley's "entourage" was that her mum visited the set one day for an hour or two.— mark romanek (@markromanek) May 30, 2016

Lorene Scafaria, the writer-director with worked with Knightley on Seeking a Friend for the End of the World, echoed Romanek's comments.

"I agree with Mark," she wrote. "Keira was a joy to work w/ [with]. Present & easy & really, really good at her job. Just lovely."

Screenwriter Massy Tadjedin, who worked with Knightley on both Last Night and The Jacket, tweeted, "I've worked with Keira twice and couldn't find John Carney's remarks more untrue or inelegant. They reveal so much more about him than her."

What you need, as an actor, or any artist, is trust. From these unfortunate remarks, I doubt John Carney ever engendered that.— Massy Tadjedin (@MTadjedin) May 30, 2016

As for the mention of an "entourage," Keira doesn't have one. But it clearly still stands out when a woman employs even a single person.— Massy Tadjedin (@MTadjedin) May 30, 2016

There are actors that directors won't call again for whatever reason. But don't disparage them in the press. C'mon. https://t.co/piMhqwyWIX— Ava DuVernay (@AVAETC) May 29, 2016