Barack Obama made a behind-the-scenes admission that Kamala Harris is failing to mobilise black voters as he held a rally in the must-win state of Pennsylvania.

In a surprise stop before the rally at a campaign field office in Pittsburgh, Mr Obama appealed directly to black men, whose support polls show Harris has struggled to capture.

“My understanding, based on reports I’m getting from campaigns and communities, is that we have not yet seen the same kinds of energy and turnout in all quarters of our neighbourhoods and communities as we saw when I was running,” Mr Obama said, adding that it “seems to be more pronounced with the brothers”.

Saying he had some “truths” that he wanted the black community to hear, Obama said that “you’re coming up with all kinds of reasons and excuses, I’ve got a problem with that”.

“Because part of it makes me think – and I’m speaking to men directly – part of it makes me think that, well, you just aren’t feeling the idea of having a woman as president.”

The address to Democrat volunteers are a sign of major nerves inside the party over support among black voters, which polls show has fallen since Joe Biden’s 2020 election victory.

Early voting has already begun in Pennsylvania, a critical swing state that could win or lose the election for both camps.