Stockholm, Sweden - Swedish climate activist Greta Thunberg on Friday labeled Donald Trump the "more dangerous" option in next week's US presidential election but slammed the incumbent administration for its support of Israel's war on Gaza.

With the US heading to the polls on November 5, the 21-year-old activist said in a post on X that it was "probably impossible to overestimate the consequences this specific election will have for the world and for the future of humanity".

"There is no doubt that one of the candidates – Trump – is way more dangerous than the other," Thunberg said.

But she also slammed sitting President Joe Biden and Vice President Kamala Harris – who is running against former President Trump – for their backing of Israel and its offensive in Gaza.

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"Let's not forget that the genocide in Palestine is happening under the Biden and Harris administration, with American money and complicity," Thunberg said.

"It is not in any way 'feminist', 'progressive' or 'humanitarian' to bomb innocent children and civilians – it is the opposite, even if it is a woman in charge."

Thunberg urged Americans to go beyond exercising their right to vote and take direct action such as protests and boycotts against the "catastrophic consequences of American imperialism".

"My main message to Americans is to remember that you cannot only settle for the least worst option," Thunberg said.