Malcolm Turnbull has defended the cartoonist Bill Leak, saying he is not a racist.

When asked on 3AW radio on Friday if Leak was racist, the prime minister laughed quickly and said: “Of course not.

“No look, he’s an Australian, he’s a cartoonist, he is a controversialist, that’s what he does. He is a very colourful, passionate Australian of enormous artistic ability.

“Bill is a very engaging guy. He writes as colourfully and powerfully as he paints.”

Leak is being investigated by the Human Rights Commission for breaching 18C of the Racial Discrimination Act for a cartoon he drew for the Australian newspaper.

The controversial cartoon shows an Aboriginal policeman returning an Aboriginal boy by the scruff of the neck to the boy’s father, who is also Aboriginal. The father is holding a beer can and cannot remember his son’s name.

Leak says he drew his cartoon in response to a Four Corners story on the Don Dale detention centre in the Northern Territory, and its treatment of Indigenous children.

“A lot of these kids are coming from the most desperate circumstances,” he told the ABC’s Lateline program this month.

“I thought to myself, ‘Well, it comes back ultimately to parents.’ We all know that’s true.

“I think a lot of people have got this idea that our Aborigines are sort of safely tucked away in remote communities, and let’s face it, not many of us city dwellers venture out there and actually see for ourselves what’s going on.”

Leak has railed against section 18C of the Racial Discrimination Act, calling it an “abomination”.

“I can only assume that a lot of people genuinely believe that freedom of speech means the legal right to hurl abuse,” he told the ABC this month. “In fact, nothing could be further from the truth.

“Freedom of speech is what created our civil and free society. It is all about the exchange of ideas, about letting people express their views in the marketplace of ideas.”

On Friday Turnbull said he had no plans to amend 18C but that the Liberal senator Dean Smith had recommended it be looked at by a parliamentary committee, and the government was considering the proposal.

“[Dean’s] made the argument, and I think it’s a reasonable one, that there should be an open, if you like, calm, cool discussion of the issues relating to this,” Turnbull said.

Turnbull, who has had his portrait painted by Leak, would not say if he thought 18C was working as it should.

He said only that there had been a lot of controversy about some applications of it.

“I’m not going to comment on a particular case that is under consideration by the Human Rights Commission,” Turnbull said.

“The point is that it is a contentious area.”