The top infectious disease official in the United States has said that health officials are seeing a "disturbing surge" of Covid-19 infections in states such as Florida, Texas and Arizona.
Dr Anthony Fauci said that part of the reason for the rise in infections is an increase in community spread.
"Right now the next couple of weeks are going to be critical in our ability to address those surges we are seeing in Florida, Texas, Arizona, and other states," he said.
He and other Trump administration officials who oversee the government response to the pandemic are testifying before a Congressional committee in Washington.
Asked about US President Donald Trump's claim that he had asked for coronavirus testing to be slowed, Dr Fauci said: "None of us have ever been told to slow testing and in fact we'll be doing more testing."
He also said he is "cautiously optimistic" that a coronavirus vaccine could be ready by the end of the year.
US virus death toll rises to over 120,000
The US has passed the grim benchmark of 120,000 deaths from the outbreak after it added another 425 fatalities in 24 hours, according to figures from Johns Hopkins University.
The world's largest economy is the hardest-hit country by the pandemic, with more than 2.31 million official cases - out of which about 640,000 people have fully recovered, according to the Baltimore-based institution.
The previous day's toll of 305 deaths in 24 hours was one of the lowest in months, but numbers have tended to be lower during the weekend and just after, depending on the feedback from local health authorities.
Many states have largely lifted lockdown measures, and New York - the country's epicentre for the pandemic - took a big step yesterday by allowing non-essential businesses to reopen.
But some 20 states, primarily in the south and west, have seen a rebound in infections.
Among them, Florida passed 100,000 cases, of which nearly 3,000 were diagnosed yesterday alone, according to local health officials.
President Trump said that the virus death toll in the US could surpass 150,000, though he insisted that two to four million lives would have been lost if the country had not taken steps to slow the spread of the disease.