U.S. President Donald Trump met with the top national security advisers of South Korea and Japan in Washington.

The White House said Thursday that Trump met briefly the day before with South Korea's National Security Adviser Chung Eui-yong and his Japanese counterpart Shigeru Kitamura.

The White House said Trump noted that the two countries are among the strongest U.S. allies in the Indo-Pacific and expressed appreciation for the "support and deep friendship" the U.S. shares with both countries.

Chung often visits the U.S. for talks with the president's national security adviser, but his meeting with Trump is considered unusual. 

The Wednesday meeting was reportedly unscheduled and came as Washington deals with Iran-related issues after Tehran's missile attacks on Iraqi bases housing U.S. troops earlier this week.

The meeting comes after Washington asked Seoul to send forces to participate in the U.S.-led military campaign in the Strait of Hormuz. Seoul has thus far taken a cautious approach to the matter.

Meanwhile, the White House National Security Council tweeted that National Security Adviser Robert O'Brien had "great bilateral and trilateral meetings" with his Korean and Japanese counterparts.

It said that discussions covered Iran, North Korea-related developments and the importance of trilateral security cooperation.