Hollywood star George Clooney has slammed US President Donald Trump for sarcastically claiming that he "made Juneteenth famous".

Juneteenth, which fell on June 19, is a day that marks the emancipation of those who had been enslaved in the United States.

Clooney will also be donating $500,000 to the Equal Justice Initiative. He said his donation was a response to Trump's claim, reports people.com.

"Thank you President Trump for 'making Juneteenth famous'. Much like when Bull Connor made 'Civil Rights' famous. My family will be donating 500 thousand dollars to the Equal Justice Initiative in honour of your heroic efforts," read Clooney's statement.

Clooney's remarks come after Trump boasted in a recent interview in the Wall Street Journal saying that he had made the June holiday "very famous" while discussing his decision to host a campaign rally in Oklahoma amid ongoing Black Lives Matter protests.

"I did something good: I made Juneteenth very famous. It's actually an important event, an important time. But nobody had ever heard of it," Trump told the newspaper.

This isn't Clooney's first time speaking out about the issue of systemic racism in the US.

Earlier this month, Clooney penned an essay about the fight against systemic racism following the death of George Floyd, saying that racism is the "greatest pandemic" of the US, and there hasn't been a "vaccine" for it even after 400 years.

In the essay, published by Daily Beast, Clooney called for "systemic change" in the US to tackle the problem of racism.