Seoul and Washington have begun annual war games, prompting the South Korean president, Moon Jae-in, to warn North Korea against using them as an excuse to intensify the "vicious cycle” of tensions.
Tens of thousands of South Korean and US troops are taking part in the Ulchi Freedom Guardian joint military drills, a largely computer-simulated exercise that runs for two weeks in the South.
The exercises are viewed by nuclear-armed Pyongyang as a provocative rehearsal for invasion, and it always meets them with threats of strong military counteraction. It said recently it was considering firing a salvo of missiles towards the US Pacific territory of Guam.
Moon described the exercises as "purely defensive in nature” and told Pyongyang it "must not use it as an excuse to launch provocations that will worsen the situation”.
"North Korea must understand its repeated provocations are what is forcing South Korea and the US to conduct the joint defensive drills, which in turn keeps the vicious cycle going,” the president told a cabinet meeting.
Pyongyang tested two intercontinental ballistic missiles last month that appeared to bring much of the US within range.
The North Korea leader, Kim Jong-un, delayed the Guam strike plan last week, but warned it could go ahead depending on Washington’s next move.
While the allies are pushing ahead with the exercises that date to 1976, about 17,500 US troops will participate in the drills –fewer than last year.
South Korean media suggested the US was considering scrapping a plan to bring in two aircraft carriers to the peninsula.
But the US defense secretary, James Mattis, said on Sunday the reduced troop numbers were "by design to achieve the exercise objectives”, denying suggestions Washington had sent fewer soldiers to try to ease tensions with Pyongyang.
"This is an exercise to make certain that we’re ready to defend South Korea and our allies over there,” he said.
The US Pacific command chief, Adml Harry Harris, arrived in South Korea on Sunday to inspect the exercises and discuss growing North Korean nuclear and missile threats.
On the eve of the drills, North Korea said the US was "pouring gasoline on fire”.
In a commentary carried by the Rodong Sinmun newspaper, Pyongyang warned of an "uncontrollable phase of a nuclear war” on the peninsula, which would entangle the US mainland.
"If the United States is lost in a fantasy that war on the peninsula is at somebody else’s doorstep far away from them across the Pacific, it is far more mistaken than ever.”
