Anthony Fauci, U.S.'s top infectious disease expert, said political divisiveness contributed significantly to the "stunning" U.S. COVID-19 death toll, which on Monday surpassed 500,000 lives lost.

In an interview with Reuters, Fauci on Monday said the pandemic arrived in the United States as the country was riven by political divisions in which wearing a mask became a political statement, rather than a public health measure.

"Even under the best of circumstances, this would have been a very serious problem," Fauci said, noting that despite strong adherence to public health measures, countries such as Germany and the UK struggled with the virus.

"However, that does not explain how a rich and sophisticated country can have the most percentage of deaths and be the hardest-hit country in the world," said Fauci, director of the National Institute of Allergy and Infectious Diseases and a top adviser to President Joe Biden. "That I believe should not have happened."