The United States has cancelled a major joint amphibious exercise with South Korea scheduled for next month because of limited U.S. military forces due to the war in Iran.

The biennial Ssangyong drills are designed to strengthen combined operations between South Korean and U.S. Marine forces through amphibious landing exercises.

The cancellation comes after President Donald Trump ordered the separate Ulchi Freedom Shield exercises to be shortened from 11 days to five, citing their cost and concerns about sending a hostile signal to North Korea.

U.S. and South Korean officials are continuing discussions about when the amphibious exercise could resume, Euro News has reported.

The moves come as Trump seeks to improve relations with North Korean leader Kim Jong-un, despite concerns over Pyongyang’s growing nuclear arsenal.