US and South Korean troops start drills amid standoff with Pyongyang

Marines of the US, left, and South Korea wearing blue headbands on their helmets, during last year's drills. Photo / AP file

US and South Korean troops have begun annual drills that come after tensions rose over North Korea's two intercontinental ballistic missile tests last month.

The Ulchi Freedom Guardian drills that began today are largely computer-simulated war games and will run until August 31.

Pyongyang calls the 11-day drills a "reckless" invasion rehearsal that could trigger the "uncontrollable phase of a nuclear war".

South Korea's President Moon Jae In said the drills are defensive in nature. He says the drills are held regularly because of repeated provocations by North Korea.

Earlier this month, US President Donald Trump pledged to answer North Korean aggression with "fire and fury". North Korea, for its part, threatened to launch missiles towards the American territory of Guam but then retracted the plan.

The exercise will bring together as many as 50,000 South Korean soldiers and approximately 17,500 US service members for a computer simulation of war on the Korean Peninsula.

The exercise is "to make certain that we're ready to defend South Korea and our allies," US Defence Secretary James Mattis told reporters yesterday.

The war games take place every year and invariably anger Pyongyang, which views such drills as a rehearsal for an invasion.

The number of US troops participating this year is lower than last year. Mattis denied that it had been scaled back in response to recent events.

In an editorial published yesterday, the official North Korean newspaper Rodong Sinmun criticised the joint military exercise as an "expression of enmity," adding that no one can guarantee "that the exercise won't lead to hostilities".

It said: "If the United States is lost in a fantasy that war on the peninsula is at somebody else's door far away from them across the Pacific, it is far more mistaken than ever".

- DPA, AAP