Athens, Greece - Swedish climate campaigner Greta Thuberg hit back at Donald Trump after the US president mocked her as "angry" and "crazy" for her pro-Palestinian advocacy.

Thunberg was detained by Israeli forces who last week stopped an international humanitarian flotilla from breaking the illegal blockade of Gaza.

The 22-year-old was released on Monday and arrived in Greece along with 170 other participants in the mission, amid shocking allegations of mistreatment in Israeli detention.

Asked about Thunberg at an Oval Office press conference, Trump called her "just a troublemaker."

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"She has an anger management problem. I think she should see a doctor," he continued. "Have you ever watched her? She's a young person. She's so angry, she's so crazy. You can have her."

On Tuesday, Thunberg responded to Trump's "flattering opinions" in a withering Instagram post.

"I would kindly receive any recommendations you might have to deal with these so-called 'anger management problems,' since – judging by your impressive track record – you seem to be suffering from them too," she wrote.

At a press conference in Athens, Thunberg centered the plight of Palestinians, whom Israel is subjecting to famine and genocide, per a growing consensus of experts.

"Let me be very clear. There is a genocide going on," she said, per Reuters. "Our international systems are betraying Palestinians. They are not even able to prevent the worst war crimes from happening. What we aimed to do with the Global Sumud Flotilla was to step up when our governments failed to do their legal obligation."

Successive US administrations have enabled the two-year-long destruction of Gaza, and the families of detained and disappeared American citizens who were on the flotilla say they've had no help from US authorities.

Mike Huckabee, Trump's ambassador to Israel, instead slandered the humanitarian mission as "Hamas-funded" in an X post.