U.S. President Joe Biden led Americans in observing a moment of silence on Monday to commemorate the grim milestone of 500,000 U.S. deaths from COVID-19, urging Americans to set aside partisan differences and fight the pandemic together.

"Today we mark a truly grim, heartbreaking milestone - 500,071 dead. That's more Americans who have died in one year in this pandemic than in World War One, World War Two and the Vietnam War combined," he said.

Biden, Vice President Kamala Harris, first lady Jill Biden and second gentleman Doug Emhoff marked a moment of silence at 6:15 p.m. ET at the White House after the president's remarks.

"As a nation, we can't accept such a cruel fate. While we've been fighting this pandemic for so long, we have to resist becoming numb to sorrow," Biden said in an emotional address at the White House.

Biden also ordered that all flags on federal properties and military facilities be lowered to half-staff for the next five days, White House spokeswoman Jen Psaki said.

The president called on Americans to remain vigilant in fighting the pandemic by continuing to wear marks, observe social distancing and receive vaccinations when it was their turn.

"We must end the politics of misinformation that have divided families, communities and the country. It's cost too many lives already," he said. "We have to fight this together as one people, as the United States of America."

About 19% of total global coronavirus deaths have occurred in the United States, an outsized figure given that the nation accounts for just 4% of the world’s population.

The country has the highest overall death figure, reflecting the lack of a unified, national response last year, when the administration of former President Donald Trump mostly left states to their own devices in tackling the greatest public health crisis in a century.

Biden, a Democrat, took office on Jan. 20 after defeating Trump, a Republican, in the 2020 presidential election, in part by arguing he would do a better job of addressing the pandemic.

Trump downplayed the pandemic in its early stages and repeatedly predicted rosier numbers about the expected death toll in the United States than came to fruition.

(Reporting by Jeff Mason; Additional reporting by Andrea Shalal; Editing by Heather Timmons and Peter Cooney )