Will this year’s massive military exercise finally provoke North Korea?

The United States military is preparing to launch a major military exercise with South Korea in coming days and faces a dangerous balancing act: How do you reassure allies in the region that you are ready for a war with North Korea without provoking an actual conflict in the process?

The annual Ulchi-Freedom Guardian exercise is scheduled for 10 days beginning August 21, and will include about 25,000 US troops and tens of thousands of South Koreans. The exercise focuses on defending South Korea against an attack from the North, and each year triggers threats and rebukes from North Korea. But it comes at an especially sensitive time now, following the exchange of a series of threats between President Donald Trump and North Korea.

US Forces Korea, the command that oversees some 28,500 American military personnel on the Korean Peninsula, has no current plans to change the size, format, or messaging for this year's exercise, said Army Colonel Chad G. Carroll, a military spokesman in South Korea. The mission is planned well in advance, considered defensive in nature, and allows both military forces and civilian officials to strengthen their readiness for a crisis, he said.

"Our job is provide our leadership with viable military options if called upon, and exercises like this hone our ability to do that," Carroll said.

North Korea this week denounced the exercise, warning that even an accident in the midst of it could trigger a nuclear conflict. But the war game also has drawn scrutiny this year from Russia and China, which have suggested cancelling the operation to alleviate tensions. The US has rejected that option, saying the exercise is needed to deter North Korean aggression as Washington seeks peaceful means to stop Pyongyang's nuclear weapons development.

"This is why we have military capability that undergirds our diplomatic activities," said Marine General Joseph F. Dunford, the chairman of the Joint Chiefs of Staff, during an appearance August 14 in Seoul. "These threats are serious to us, and thus we have to be prepared."

On August 15, North Korea appeared to ease up on a threat to shoot missiles toward the US island territory of Guam. A state-run media outlet reported that North Korean leader Kim Jong Un said he would watch the US "a little more" rather than responding quickly, but would "make an important decision, as it already declared", if the "Yankees persist in their extremely dangerous reckless actions on the Korean Peninsula and in its vicinity." The report came hours after US Defense Secretary Jim Mattis warned that if North Korea hits the US island territory of Guam with a missile, it would be "game on", meaning war.

Secretary of State Rex Tillerson declined to respond directly to Kim's decision to pull back from his threat to launch missiles toward Guam, but said the door to talks remains open.

"We continue to be interested in finding a way to get to a dialogue, but that's up to him," Tillerson said at the State Department.

Tillerson and Mattis jointly host their Japanese counterparts in Washington August 17, with North Korea at the top of the agenda.

Army Colonel Robert Manning, a Pentagon spokesman, said the US and South Korea have "made a lot of progress" in recent years to prepare against any North Korea threat. Ulchi-Freedom Guardian is a big part of that, with two other related exercises, Foal Eagle and Key Resolve.

The US-South Korean military exercises have exacerbated tensions in the past. In March, the beginning of Foal Eagle prompted North Korea to test-fire four ballistic missiles, which in turn prompted the Pentagon to announce that it was assembling a missile defence system known as Terminal High Altitude Area Defence (Thaad) on the Korean Peninsula with approval of the Government in Seoul.

In 2015, Ulchi-Freedom Guardian came shortly after an August 4 attack in which two South Korean soldiers stepped on landmines in the heavily militarized border region with North Korea, known as the Demilitarized Zone. South Korea vowed to retaliate, and the two Koreas exchanged artillery and rocket fire over the border during Ulchi-Freedom Guardian after South Korea began broadcasting propaganda messages over the border and North Korea responded by turning on its own loudspeakers.

The exercise itself has changed several times, and dates back to 1968, when South Korea and the US created a war game called Focus Lens. That occurred after North Korea hijacked a US Navy intelligence ship, the USS Pueblo, and launched a bloody Special Operations raid on the Blue House, the centre of the South Korean government, with plans to kill South Korean President Park Chung Hee.