SEOUL (AFP) - North Korea on Sunday (Aug 20) blasted an annual joint military exercise starting Monday (Aug 21) as an act of "adding fuel to the fire" amid heightened tensions on the Korean Peninsula, reported South Korea's Yonhap news agency.

The Rodong Sinmun, the official newspaper of North Korea's ruling party, said in an editorial the US moves to place the worst-ever sanctions on it and launch military provocations have made the situation on the peninsula extremely tense.

The allies' Ulchi Freedom Guardian (UFG) exercise will kick off on Monday and run until Aug 31. Unlike the field training "Foal Eagle" exercises held earlier this year, the UFG is almost entirely composed of computer simulations that take place in bunkers and tents hidden from view, said Stars and Stripes in an article published over the weekend.

Admiral Harry Harris, commander of the U.S. Pacific Command and the top U.S. military official in charge of the Asia-Pacific region, arrived in South Korea on Sunday (Aug 20) to observe the UFG exercises.

Following his meeting with South Korea's defence minister Song Young Moo on Sunday (Aug 20), both men agreed to step up joint efforts to counter North Korea's threats.

Adm Harris also met General Jeong Kyeong Doo, South Korea's new top military officer who was inaugurated on Sunday.

Analysts say all eyes will be on the annual war game in the South this week that could send tensions spiralling back upwards after the war of words between the US and North Korea appeared to have cooled off slightly.

The 11-day exercise will be the first major exercises since North Korea test-fired two intercontinental ballistic missiles (ICBMs) last month (July) that appeared to bring much of the US within range. Its ICBM tests triggered an intense warning by President Donald Trump that Washington could rain "fire and fury" on the North.

Pyongyang then threatened to fire a salvo of missiles towards the US territory of Guam - a plan that leader Kim Jong Un last week said was delayed, but warned could go ahead depending on Washington's next move.

The North's reaction to the "Ulchi Freedom Guardian" (UFG) joint military exercise that starts on Monday (Aug 21) will be key to determining what happens next.

US top military official Joseph Dunford, US Joint Chiefs of Staff Chairman, said last week the United States and South Korea would go ahead with joint military drills despite pressure from North Korea and its main ally, China, to halt the contentious exercises that Pyongyang routinely describes as preparation for war.

The Pentagon said on Friday the joint exercise, dubbed Ulchi Freedom Guardian, would involve about 17,500 US service members as well as troops from Australia, Canada, Colombia, New Zealand, the Netherlands and Britain.

In a piece published on the Stars and Stripes website, the number of US service men and women involved in this year's exercise is "a sharp decrease from the 25,000 who participated last year and the lowest number in at least five years". The South is fielding around 50,000 troops this year, similar to that of last year.

US Forces Korea rejected any link between the numbers and current events.

"We are not changing the exercise based on any recent activities. This is an annual exercise, planned for months in advance," USFK spokesman Col. Chad Carroll said in an email.

But some analysts suggested it could be another step towards de-escalating tensions that skyrocketed as North Korea and Trump lobbed threats at each other in a war of words.

The way in which the games are conducted and advertised will send an important signal to the North, said the US military's newspaper in the piece titled "What to watch for as war games begin between US, South Korea".

Experts said the military could simultaneously deploy US supersonic bombers or aircraft carriers in a show of force if it wanted to project strength, or show restraint to calm the situation.

"It will be interesting to see how high a profile these exercises get," said James Schoff, a senior fellow at the Carnegie Endowment for International Peace.

"Are we trying to publicise them and put some kind of military psychological pressure on (NORTH KOREA), or will we keep it low key and business like?"

"The latter would suggest that we think a low key approach might encourage NK restraint and eventually open a door to dialogue," he added in an e-mail to Stars and Stripes.

North Korea has long denounced the drills, calling them rehearsals for a northern invasion.

"The joint exercise is the most explicit expression of hostility against us, and no one can guarantee that the exercise won't evolve into actual fighting," the Rodong Sinmun report 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," it also said.

Separately, Pyongyang's propaganda website Uriminzokkiri said in a commentary that the U.S. and South Korea are staging an exercise to try to wage a nuclear war around the Koran Peninsula, warning,

"The North Korean army is placing the South Korean military in its crosshairs."

South Korea's new top military officer on Sunday issued a stern warning to the North, saying it will face merciless retaliation for any attack, reported Yonhap.

General Jeong, chairman of the Joint Chiefs of Staff (JCS), stressed that the current security conditions on the peninsula are "more serious than at any other time" amid the North's fast-advancing nuclear and missile programmes. He said he will focus efforts on establishing a "full range of defense postures" to counter all types of threats.

"If the enemy provokes, (our military) will retaliate resolutely and strongly to make it regret bitterly," said Jeong, who was inaugurated on Sunday (Aug 20).

Speaking during a change of command ceremony held at the Ministry of National Defense compound in Seoul, he added deterrence based on combat readiness is a priority.

Jeong, formerly an Air Force chief of staff and fighter jet pilot, replaced Army General Lee Sun Jin, who retired after a 42-year service.

Jeong is South Korea's first JCS leader hailing from the Air Force in 23 years, according to Yonhap.