The United States has canceled a major amphibious landing exercise with South Korea scheduled for next month, citing constraints on the availability of American forces because of the ongoing war in Iran, South Korea’s Marine Corps said Monday.

The U.S. Marine Corps formally notified its South Korean counterpart in June that it would be unable to provide sufficient forces for the division-level exercise, known as Ssangyong, or “Twin Dragons.”

A South Korean Marine Corps spokesperson said the two allies remain in close consultation about resuming the drills but did not provide details on how they might compensate for lost training opportunities or prevent similar cancellations.

U.S. Forces Korea did not immediately comment on the cancellation.

The development comes amid growing concerns about the impact of Washington’s military commitments in the Middle East on its ability to maintain operations and readiness elsewhere.

Later Monday, U.S. Secretary of State Marco Rubio spoke with South Korean Foreign Minister Cho Hyun about a range of issues affecting the alliance.

According to the State Department, Rubio stressed the importance of close coordination between Washington and Seoul on matters central to their longstanding security partnership.

The cancellation of Ssangyong follows President Donald Trump’s surprise decision to significantly scale back another annual U.S.-South Korean military exercise that concluded last Friday.

Trump cited the cost of the drills as well as South Korea’s refusal to participate in the U.S. war against Iran when ordering the reduction.

The latest changes to joint military exercises come as Washington and Seoul seek to balance military preparedness on the Korean Peninsula with increasing demands on U.S. forces in other parts of the world.