Ukraine's leader Volodymyr Zelenskyy says he can 'forget' Joe ...

Ukraine's President Volodymyr Zelenskyy has said he can "forget" Joe Biden's gaffe where he introduced him as "President Putin".

The US leader made the blunder on Thursday at a NATO summit in Washington DC, and in another high-profile mistake hours later he referred to his number two, Kamala Harris, as "Vice President Trump" at a news conference.

Asked during a visit to Ireland on Saturday about Mr Biden's Putin mishap, Mr Zelenskyy told reporters: "It's a mistake. I think United States gave a lot of support for Ukrainians. We can forget some mistakes, I think so."

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At the Washington summit, NATO members pledged $43bn (£33bn) in military aid for Ukraine next year as it defends itself from Russia's full-scale invasion and attempts to deter future aggression.

There were new promises of air defence support, including Patriot missile systems and F-16 fighter jets.

The latest gaffes by Mr Biden have heaped further pressure on the 81-year-old who is facing calls from within his own party to step aside as the Democrat nominee in the White House race amid concerns about his age and fitness to serve.

An NPR/PBS poll released on Friday found Mr Biden leading his 78-year-old Republican rival Donald Trump 50% to 48%.

That is a slight rise from his position before a 27 June debate, where the president seemed to lose his train of thought and his voice trailed off several times.

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Mr Biden has repeatedly said he intends to stay in the contest ahead of November's election.

And he retains support from key figures in the party, including California Governor Gavin Newsom, a prominent Democrat who is tipped as a possible presidential nominee in future.

Read more:Analysis - Biden blew reset momentPresident Biden's various gaffes over the years

During a boisterous performance at a rally in Detroit on Friday, Mr Biden insisted: "I am running and we're going to win."

"I'm the nominee," he said. "I'm not going anywhere.

"It's time for us to stop treating politics like it's entertainment or a reality TV show."

And to wild cheers, he shouted: "Donald Trump is a loser!"

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Mr Biden also warned Project 2025, a conservative policy platform that would seek to slash the federal government if Mr Trump is elected, was "deadly serious".

Since the 27 June debate, at least 19 Democrats in Congress have urged Mr Biden to step aside so the party can pick another candidate, as have some donors, Hollywood stars, activist groups and news outlets.

Around $90m (£80m) in donation pledges will remain on hold as long as he remains in the race, the New York Times has reported.