Former President Donald Trump said on Thursday that he is unsure how to react to Russian President Vladimir Putin's endorsement of Kamala Harris, questioning whether he should feel offended or appreciative.

"He [Putin] endorsed Kamala, and I didn't know if I was supposed to call him up and say 'Thank you very much,' but he endorsed Kamala... I don't know exactly what to say about that. I don't know if I'm insulted or he did me a favor," Trump said during an event at the Economic Club of New York.

This comes shortly after Putin said during a statement at the Eastern Economic Forum on Thursday that he favors Kamala Harris over Trump. However, the ultimate decision rests with the American people in choosing their president, he said.

White House National Security Communications Advisor John Kirby responded by saying that Putin should avoid making any comments regarding US presidential elections.

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Back in February, Putin characterized his US counterpart, Joe Biden, as being more "predictable" compared to Donald Trump, but asserted that the Kremlin is ready to collaborate with whoever emerged as the victor in November's election.

When asked by a journalist about Russia's preference between the likely contesting candidates, the Democratic incumbent and Republican frontrunner Trump, Putin stated, "Biden, he's more experienced. He's predictable, he's an old-school politician."

Putin dismissed inquiries regarding Biden's age and health, even though the president is set to turn 82 just weeks after the election.

"When I met Mr Biden three years ago, it's true, people were already talking about his inabilities, but I saw nothing of the sort," said Putin, evidently referring to a summit in Geneva.

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Earlier this year, an investigation conducted by three American journalists revealed that the US intelligence community fabricated claims suggesting that Putin favored Donald Trump over Hillary Clinton in the 2016 US presidential election.

In January 2017, an Intelligence Community Assessment (ICA) released by the US Director of National Intelligence suggested that Putin preferred Trump to win the election.

However, after a thorough investigation, journalists Michael Shellenberger, Matt Taibbi, and Alex Gutentag found that the authors of the assessment fabricated intelligence regarding this claim.

The information was sourced from people close to a House Permanent Select Committee on Intelligence (HPSCI) investigation into the origins of the Trump-Russia scandal.

The report further states that the release of the HPSCI investigation findings is being obstructed.