Joe Biden has called his presumptive rival for the US presidency Donald Trump a “fool” who was “stoking deaths” with his stance on wearing face masks amid the pandemic.
Mr Biden wore a facial covering during his first public appearance in more than two months at a Memorial Day wreath laying in Delaware.
White House incumbent Mr Trump retweeted a post which appeared to make fun of Mr Biden’s precautions against Covid-19.
In an interview with CNN, Mr Biden responded: “He’s a fool, an absolute fool, to talk that way.”
“He’s supposed to lead by example.”
The former vice president also noted that nearly 100,000 Americans have been killed by the virus and suggested that as many as half of those deaths were avoidable but for Mr Trump’s “lack of attention and ego”.
Officials have recommended that people cover their nose and mouth in public when other measures, such as practising social distancing of at least 1.8 metres, are not possible.
But the issue has become increasingly politically charged, with Mr Trump refusing to wear a mask and polls finding that conservative Americans are more likely to forgo them as well.
Mr Biden did not wear a mask during the CNN interview, which was conducted outside his house, but he sat more than three metres from the reporter.
“It’s just absolutely this macho stuff,” Mr Biden said of Mr Trump bristling at wearing a mask in public, a practice the former vice president called being “falsely masculine”, adding: “It’s cost people’s lives.”
After Mr Biden wore a mask on Memorial Day, the president retweeted a post by a political commentator that featured an image of a masked Mr Biden over the comment: “This might help explain why Trump doesn’t like to wear a mask in public.”
Asked about that during a subsequent event in the White House Rose Garden, the president responded: “Biden can wear a mask.
“But he was standing outside with his wife, perfect conditions, perfect weather.
“They’re inside, they don’t wear masks and so I thought it was very unusual that he had one on. But I thought that was fine. I wasn’t criticising him at all. Why would I ever do a thing like that?”