US President Joe Biden on Thursday mistakenly referred to Ukrainian President Volodymr Zelensky as "President Putin" before correcting himself at the Nato summit in Washington.

"And now I want to hand it over to the president of Ukraine, who has as much courage as he has determination, ladies and gentlemen, President Putin," Biden said, referring to Zelensky, before correcting himself.

"Going to beat President Putin, President Zelensky. I am so focused on beating Putin," Biden said while correcting himself.

The room at the summit gasped when Biden misidentified Zelensky as Putin.

Biden has been under intense scrutiny in recent days and has faced doubts, including from members of his own Democratic Party, about his reelection chances after a weak and faltering performance in a debate late last month against Republican former President Donald Trump.

Later on Thursday, Biden plans to hold a solo press conference at the Nato summit, his first time facing the press alone since November.

Biden's remarks on Thursday came as Nato members extended support to Ukraine to combat the Russian assault that began in February 2022.

The United States has been Ukraine's most important partner in military assistance amid the war. (Reuters)