An emotional US President Joe Biden called the milestone of more than 500,000 US deaths from Covid-19 "heartbreaking" and urged the country to unite against the pandemic. "I know what it's like," Mr Biden said in a national television address, referring to his own long history of family tragedies. "I ask all Americans to remember, remember those we lost and those they left behind," he said. "I also ask us to act, to remain vigilant, to say socially distant, to mask up, to get vaccinated." Mr Biden, accompanied by his wife Jill and Vice President Kamala Harris and her husband Doug Emhoff, then stood outside the White House to mark a moment's silence in front of 500 candles representing the huge toll.