SEOUL, South Korea (AP) — The United States began a large military exercise with South Korea involving thousands of troops Monday while also waging an escalating war in the Middle East.

South Korea’s Joint Chiefs of Staff has said about 18,000 Korean troops will take part in Freedom Shield, which runs through March 19. U.S. Forces Korea hasn’t confirmed the number of American troops participating in the training in South Korea.

The allies’ combined exercise comes amid South Korean media speculation that Washington is relocating some assets from South Korea to support fighting against Iran.

U.S. Forces Korea said last week it would not comment on specific movements of military assets for security reasons. South Korean officials also declined to comment on the reports that some U.S. Patriot anti-missile systems and other equipment were being moved to the Middle East, but they said there would be no meaningful impact on the allies’ combined defense posture.

Freedom Shield may trigger an irritated response from North Korea, which has long described the allies ’ joint exercises as invasion rehearsals and used them as a pretext to ramp up its own military demonstrations and weapons tests. The allies say the drills are defensive in nature.

North Korea has suspended all meaningful dialogue with Washington and Seoul following the 2019 collapse of a summit between leader Kim Jong Un and U.S. President Donald Trump during his first term. Tensions rose in recent years as Kim used Russia’s invasion of Ukraine as a window to accelerate the development of his nuclear arsenal and increase his leverage by aligning militarily with Moscow, which has received thousands of North Korean troops and large weapons shipments to help fuel its warfighting.

The allies’ drills follow a major political conference in Pyongyang last month, where Kim confirmed his hard-line view of “enemy” Seoul but left the door open to talks with Washington, calling on the United States to drop its demand for North Korea’s denuclearization as a precondition for dialogue.

Freedom Shield is one of two annual “command post” exercises conducted by the allies; the other is Ulchi Freedom Shield, held in August. The drills are largely computer-simulated and designed to test the allies’ joint operational capabilities while incorporating evolving war scenarios and security challenges. As usual, the March drill will be accompanied by a field training program, called Warrior Shield, but the number of field exercises during the Freedom Shield period has declined to 22 compared to last year’s 51.

While U.S. and South Korean militaries say field exercises are often spread out throughout the year, there’s speculation that the allies are seeking to tone down the spring drills to create conditions for dialogue with North Korea. Liberal South Korean President Lee Jae Myung has expressed a desire for diplomacy, and some of his top officials have voiced hope that Trump’s expected visit to China in late March or April could possibly create an opening with Pyongyang.