US President Joe Biden mistakenly referred to Ukrainian President Volodymyr Zelenskyy as "President Putin" during a news conference on Thursday.

Media outlets were quick to issue reports about the incident. The verbal mix-up comes as calls have been growing for the 81-year-old US president to drop his reelection bid.

Biden was speaking at a news conference after the conclusion of the NATO summit in Washington. Regarding NATO's continued support for Ukraine, Biden said, "We're united against Putin's senseless brutal war. We are united behind Ukraine."

He then introduced Zelenskyy by saying, "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 quickly corrected himself and said, "I am so focused on beating Putin."

Later on Thursday, Biden made another error. When asked by a reporter if he is confident that US Vice President Kamala Harris has the ability to serve as president, Biden mistakenly referred to Harris as his Republican rival, former President Donald Trump.

Biden said, "Look, I wouldn't have picked Vice President Trump to be vice president if she was not qualified to be president."

Trump quickly reacted to the gaffe by posting a message on social media, along with footage of the incident. He wrote, "Great job, Joe!"