The U.S. government said Thursday it will purchase and donate 500 million doses of Pfizer Inc.'s coronavirus vaccine to more than 90 lower-income countries and the African Union, an announcement that came just ahead of the Group of Seven summit meeting in Britain.

The United States hopes the move will spur a coordinated vaccination effort via cooperation between the world's wealthy democracies, the White House said, apparently in a bid to counter so-called vaccine diplomacy by China and Russia, which it has labeled as autocracies.

Photo shows vials of Pfizer Inc.'s COVID-19 vaccine. (Kyodo)

The vaccines, developed by the U.S. pharmaceutical giant and its German partner BioNTech SE, will start shipping in August, with 200 million doses to be delivered by the end of the year and the remaining 300 million to be delivered in the first half of 2022.

The United States will allocate the doses to 92 low- and lower-middle-income countries as well as the African Union, working through the U.N.-backed COVAX global vaccine sharing program, according to the White House.

The Biden administration has been beefing up efforts to help supply vaccines to other parts of the world that are struggling to contain outbreaks, already pledging to share 80 million vaccines from the U.S. supply by the end of June.

India, South Korea and Taiwan have been selected to be among the destinations to receive the first batch of the 80 million doses.

The United States has also contributed $2 billion to COVAX, which the White House says is more than any other nation, and is supporting local vaccine production capacity abroad by working with Japan, India and Australia -- collectively called the Quad.

Tackling the pandemic, which has killed more than 3.7 million people around the world, is expected to be one of the key topics to be discussed by the G-7 leaders during the three-day gathering to start Friday in the British seaside resort of Carbis Bay, Cornwall.

British Prime Minister Boris Johnson, who will chair the gathering, has said he will call on his counterparts during the gathering to make "concrete commitments" to vaccinate the entire world by the end of 2022.

The G-7 comprises wealthy democracies -- Britain, Canada, France, Germany, Italy, Japan, the United States plus the European Union.

Related coverage:

Suga to depart Japan for G-7 summit in Britain on June 10

G-7 summit to kick off June 11, likely to showcase unity against China

G-7 leaders to back Japan's efforts to stage Olympics