US President Joe Biden will announce at the upcoming Group of Seven summit that his country will donate half a billion doses of coronavirus vaccines to nearly 100 lower income countries and the African Union.
The G7 summit starts in Cornwall, England, on Friday.
White House officials say the US will purchase the vaccines from pharmaceutical company Pfizer.
They say 200 million shots will be delivered by the end of this year and 300 million in the first half of 2022.
Officials say this will be the largest-ever purchase and donation of vaccines by a single country. They say it will serve as the foundation for a coordinated effort by the world's democracies to vaccinate people.
The White House has been under mounting pressure to donate the vaccines to other countries that are desperately in need.
Analysts say the Biden administration is trying to counter Chinese and Russian vaccine diplomacy.