GYEONGJU, South Korea (AP) — The United States will share closely held technology to allow South Korea to build a nuclear-powered submarine, President Donald Trump said on social media Thursday after meeting with the country’s president.

President Lee Jae Myung stressed to Trump in their Wednesday meeting that the goal was to modernize the alliance with the U.S., noting plans to increase military spending to reduce the financial burden on America. The South Korean leader said there might have been a misunderstanding when they last spoke in August about nuclear-powered submarines, saying that his government was looking for nuclear fuel rather than weapons.

Lee said that if South Korea was equipped with nuclear-powered submarines, that it could help U.S. activities in the region.

U.S. nuclear submarine technology is widely regarded as some of the most sensitive and highly guarded technology the military possesses. The U.S. has been incredibly protective of that knowledge, and even a recently announced deal with close allies the United Kingdom and Australia to help the latter acquire nuclear submarine technology doesn’t feature the U.S. directly transferring its knowledge.

Trump’s post on social media comes ahead of his meeting with Chinese President Xi Jinping, whose country possesses nuclear submarines, and after North Korea in March unveiled for the first time a nuclear-powered submarine under construction. It’s a weapons system that can pose a major security threat to South Korea and the U.S.

As Trump visited South Korea, North Korea said Wednesday it conducted successful cruise missile tests, the latest display of its growing military capabilities.

Pentagon officials didn’t immediately respond to questions about Trump’s announcement on sharing the nuclear sub technology with South Korea.

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Boak reported from Tokyo. AP writer Konstantin Toropin contributed to this report from Washington.