SEOUL/GUAM (Reuters) - North Korea said on Thursday it was completing plans to fire four intermediate-range missiles over Japan to land near the U.S. Pacific island territory of Guam in an unusually detailed threat that further heightened tensions with the United States.

North Koreas army will complete the plans in mid-August, when they will be ready for leader Kim Jong Uns order, state-run KCNA news agency reported, citing General Kim Rak Gyom, commander of the Strategic Force of the Korean Peoples Army. The plans called for the missiles to land in the sea only 30-40 km (18-25 miles) from Guam.

The reclusive communist country, technically still at war with the United States and South Korea after the 1950-53 Korean conflict ended with a truce and not a peace treaty, is known for making bellicose threats.

But experts in the United States and South Korea said North Koreas plans ratcheted up risks significantly, since Washington was likely to view any missile aimed at its territory as a provocation, even if launched as a test. North Korea has carried out a series of missile and nuclear bomb tests in defiance of the international community.

North Korea announced the plans following U.S. President Donald Trump s comments on Tuesday that any threats by Pyongyang would be met with fire and fury like the world has never seen, remarks that KCNA called a load of nonsense.

North Koreas apparently rapid progress in developing nuclear weapons and missiles capable of reaching the U.S. mainland has fueled tensions that erupted into a war of words between Washington and Pyongyang this week, unnerving regional powers and global investors.

World stocks fell for a third day, with shares in Seoul slumping to a seven-week low.

The rising tensions between North Korea and the United States the biggest foreign policy crisis Trump has faced in his six-month-old presidency spurred a broad market sell-off in U.S. stocks. By midday, the benchmark S&P 500 stock index <.spx> fell 1 percent. The index has had just two days so far this year where it has closed with losses of more than 1 percent.

If Pyongyang carries out its threat and launches missiles toward Guam, it would represent an unprecedented milestone in the already fraught relations between the United States and North Korea.

As announced by North Korea, which added detail to a plan first unveiled on Wednesday, the planned path of the missiles would cross some of the worlds busiest sea and air traffic routes.

Guam, a tropical island more than 3,000 km (2,000 miles) to the southeast of North Korea, is home to about 163,000 people and a U.S. air base, Navy installation that includes a submarine squadron, a Coast Guard group and roughly 6,000 U.S. military service members.

The Hwasong-12 rockets to be launched by the KPA (Korean Peoples Army) will cross the sky above Shimane, Hiroshima and Koichi Prefectures of Japan, the North Korean report said. They will fly 3,356.7 km (2,085.8 miles) for 1,065 seconds and hit the waters 30 to 40 km away fromGuam. The report did not mention any threat of the use of nuclear missiles near Guam.

Sound dialogue is not possible with such a guy bereft of reason and only absolute force can work on him, KCNA said of Trump.

Speaking to reporters in to New Jersey, White House spokeswoman Sarah Sanders said that certainly nothing has changed in the presidents thinking on North Korea given the latest developments. The White House said Trump would receive a security briefing later in the day.

U.S. Senator Lindsey Graham, a key Republican voice on foreign policy, said that based on his conversations with Trump he believes the president would be willing to launch a pre-emptive strike to prevent Pyongyang from launching a nuclear attack on the U.S. homeland.

If negotiations fail, he is willing to abandon strategic patience and use pre-emption, Graham said of Trump during an interview with radio host Hugh Hewitt. I think hes there mentally. He has told me this.

So Im 100 percent confident that if President Trump had to use military force to deny the North Koreans the capability to strike America with a nuclear-tipped missile, he would do that, Graham added.

Korea expert and former CIA analyst Robert Carlin, a visiting scholar at Stanford Universitys Center for International Security and Cooperation, said announcing a specific target was unusual for North Korea, although it had previously mentioned targeting specific South Korean military facilities.

Weve seen them talk in specific terms before, just not something as sensitive ... as an American military base, Carlin said.

ENJOY THE BEACHES

Visitors and residents on Guam appeared to be taking things in their stride. The main beach front on the island was packed with tourists dozing under trees or on the sun loungers of five-star hotels lined up before a calm sea.

Governor Eddie Calvo said Guam had experienced a Japanese invasion in World War Two and countless earthquakes and super-typhoons, and there was no U.S. community better prepared to meet the North Korean threat.

We are concerned about these threats but at the same time we also want to make sure people dont panic and go on with their lives. Enjoy the beaches, Calvo said.

Major airlines that fly over the region said they had so far made no plans to change flight paths.

The U.S. Seventh Fleet currently has six Aegis ballistic missile defense ships in the region capable of targeting North Korean missiles, and Japan has a further four. Guam also has a Terminal High Altitude Area Defense (THAAD) anti-missile system, similar to one recently installed in South Korea.

Japan could legally intercept a North Korean missile headed towards Guam, its defense minister said on Thursday, but experts believe Japan does not currently have the capability to do so.

Angered as the United States and its allies ignore Chinese calls to calm tensions over North Korea, and distracted by domestic concerns, China is largely sitting out the crisis.

Tension in the region has risen since North Korea carried out two nuclear bomb tests last year and the intercontinental missile tests, all in violation of U.N. Security Council resolutions. Trump has said he will not allow Pyongyang to develop a nuclear weapon capable of hitting the United States.

Washington has warned it is ready to use force if needed to stop North Koreas ballistic missile and nuclear programs but that it prefers global diplomatic action. The U.N. Security Council unanimously imposed new sanctions on North Korea on Saturday.

(Additional reporting by Daniel Bases in New York, David Brunnstrom in Washington, Soyoung Kim in Seoul, William Mallard, Tim Kelly, Kiyoshi Takenaka and Linda Sieg in Tokyo, Ben Blanchard and Michael Martina in Beijing, Jamie Freed in Singapore and John Ruwitch in Shanghai; Writing by Raju Gopalakrishnan and Will Dunham; Editing by Nick Macfie and Alistair Bell)