This combo shows US President Joe Biden (left) and China's President Xi Jinping. AFP

Biden also said Xi was very embarrassed when a suspected Chinese spy balloon was blown off course over US airspace early this year, making a personal comment on the Chinese leader when Blinken said on Monday the "chapter" should be closed.

It was unclear why Biden made the comments on Xi — China's most powerful leader since Mao Zedong after he secured a precedent-breaking third term as president and head of the Communist Party.

"The reason why Xi Jinping got very upset in terms of when I shot that balloon down with two box cars full of spy equipment in it was he didn't know it was there," Biden said at a fundraiser in California.

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"That's a great embarrassment for dictators. When they didn't know what happened. That wasn't supposed to be going where it was. It was blown off course," Biden added.

Biden also said China "has real economic difficulties."

Xi, who met with Blinken on Monday, has not publicly responded to Biden's comments but they are unlikely to go down well in Beijing and could jeopardise efforts by both countries to bring their relationship back to a more stable footing after the balloon incident.

Reuters