Seoul's unification ministry spokesman Baek Tae-hyun told a press briefing that the authorities of South Korea and the United States were closely watching relevant moves in preparation for the DPRK's "further provocation".
Guam Gov. Eddie Calvo said he discussed the situation with representatives of the White House, the National Security Agency, the Pentagon and the Department of Homeland Security.
Guam's homeland security adviser, George Charfauros, urged calm and said defenses were in place after North Korea is reviewing plans to strike US military targets in Guam with its medium-range ballistic missiles to create "enveloping fire", according to the state media Korean Central News Agency.
Guam was described by President Barack Obama's defence secretary Ashton Carter as "an important strategic hub for the United States military in the Western Pacific". The bombers have been "threatening and blackmailing" the DPRK through their frequent visits to the sky above South Korea, the KCNA said.
In response, Trump threatened the Asian country "with fire and fury".
The US territory is home to Andersen Air Force Base. I want to reassure the people of Guam that now there is no threat to our island or the Marianas.
The indigenous people are referred to as Chamorros and are considered US citizens by birth.
"Guam is American soil".
Guam is home to thousands of USA service personnel and key military bases.
Throughout the mission, which lasted about 10 hours, the aircrews practiced intercept and formation training, Pacific Air Forces officials said, enabling them to enhance their combined capabilities and tactical skills while also strengthening the long-standing military-to-military relationships in the Indo-Asia-Pacific region. "We are not just a military installation".
"I've kind of felt this is a good thing", she said.
On the streets of the capital Hagatna, there was a sense of calm.
The threat is unsurprising for the more than 160,000 people who live on the small island, roughly the size of Chicago, in the western Pacific Ocean.
The US navy last month said the multinational exercise would run until 12 August, this Saturday.
"I just have to make sure that my emergency kits are ready if Homeland Security says we should get ready". "They're going to take care of us".
While many are concerned about the recent threats by North Korea it should be pointed out that this is not the first time that North Korea has threatened Guam.