Washington DC - President Donald Trump took a sudden swipe at France on Monday during an interview with Fox News, saying "we've had a lot of problems with the French."

Far-right provocateur Laura Ingraham had questioned the US president on the enrollment of Chinese students at US universities, ranting: "They're not the French, they're the Chinese. They spy on us. They steal our intellectual property."

But Trump abruptly cut in to respond, saying: "Do you think the French are better, really? I will tell you, I'm not so sure."

The Republican has had a well-catalogued hands-on relationship with his French counterpart Emmanuel Macron, full of muscular handshakes, mutual backslapping, and knee-touching for the cameras.

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Macron in September even called Trump to tell him he was being blocked on the street by the presidential convoy in New York as he rushed to a meeting from the UN headquarters.

But the pair's bromance has occasionally been tetchy, with Trump notably opposed to Macron's recognition of a Palestinian state and climate policy.

In the Fox interview, the 79-year-old pivoted to a new bone of contention.

"We've had a lot of problems with the French where we get taxed unfairly on our technology," Trump claimed.

Trump has previously said he would impose "substantial" extra tariffs on countries that introduced "discriminatory" digital taxes.

The comments were sparked by Ingraham asking about the administration's multiple U-turns on foreign students.

Secretary of State Marco Rubio said in May that Washington would "aggressively revoke visas for Chinese students," but just a few months later, Trump said the country was going to allow as many as 600,000 to "come in."