Japan's prime minister spoke with the leaders of the United States and South Korea separately on Friday ahead of their trilateral summit near Washington.

Kishida Fumio and US President Joe Biden set out plans to develop an air defense system capable of stopping some of the world's most dangerous missiles in their tracks.

Both China and North Korea are developing advanced weapons such as hypersonic missiles, which travel about five times the speed of sound.

Kishida and Biden say their countries will improve joint deterrence and response, including the co-development of a new system to intercept those missiles.

Kishida and South Korean President Yoon Suk-yeol agreed to maintain close bilateral communication, including a strategic dialogue between their vice foreign ministers in autumn.

Tokyo and Seoul have in recent months walked a friendlier path.

Yoon said the trilateral summit did not cover the crippled Fukushima Daiichi nuclear power plant in northeastern Japan. Tokyo plans to release treated and diluted water from the facility into the ocean.

Speaking to reporters, the South Korean leader called for a transparent approach based on science.