Japan will contribute up to $500 million (about ¥62.1 billion) to U.N.-backed efforts to ensure equal access to COVID-19 vaccines, Prime Minister Fumio Kishida said Friday at a leaders' summit held to secure funding to boost the global vaccination rate.

The sum comes on top of the $1 billion already provided by Japan to the COVAX vaccine-sharing program as lower-income nations struggle to secure doses amid tight global supplies and as the pandemic drags on.

Speaking at the COVAX summit, Kishida said vaccines are a powerful tool to fight the pandemic but there remain gaps among nations in terms of access.

"The key to truly overcoming this pandemic is to ensure equitable access to vaccines in every country and region of the world so that no one's health is left behind," Kishida said in his video message.

The gathering, co-hosted by Gavi, a vaccine-focused international organization, along with Germany, Indonesia, and Senegal, comes as part of efforts to raise at least $5.2 billion in additional funding to vaccinate more people globally.

The United States was the biggest contributor in funding to the initiative as of early March, followed by Germany and Japan.

The World Health Organization is aiming to have around 70% of the world's population vaccinated by mid-2022.

So far, Japan has donated around 43 million doses either directly or via the COVAX program.