The United States has passed 600,000 deaths attributed to COVID-19, according to data by Johns Hopkins University.

The grim milestone came Tuesday amid a speed-up in the country's vaccination drive, which has drastically brought down daily cases and fatalities.

The same day, California and New York lifted most of their remaining coronavirus restrictions, reopening after more than a year.

It took nearly four months for the death toll to go from half a million to 600,000, compared to just over a month to go from 400,000 to 500,000.

President Joe Biden earlier said that while new infections and deaths in the U.S. had been dropping dramatically, too many lives were still being lost, and stressed "now is not the time to let our guard down."