In the latest show of force against North Korean leader Kim Jong-un, American bombers and Japanese and South Korean fighter jets flew over the Korean Peninsula in an overnight drill.
The bombers took off from the US Pacific territory of Guam on Tuesday night, before entering South Korean airspace and conducting firing exercises over the East Sea and Yellow Sea, South Korea's military said.
North Korea's possession of secret war plans would require a major overhaul of how South Korea and its ally Washington would respond if there's another war on the Korean Peninsula. Pyongyang has historically conducted tests on noteworthy anniversaries and holidays such as a missile test on July 4 for America's Independence Day.
North Korean hackers stole strategic plans drawn up by South Korea and the United States on how they would respond to an attack by the rogue regime as well as details of a "decapitation" plan to assassinate President Kim Jong Un, according to a report on Tuesday.
Robert Lee, a cybersecurity expert who consults with the industry, told NBC News that "any targeting of infrastructure by a foreign power is a concerning thing", but that North Korea and other adversaries "are far from being able to disrupt the electric grid".
Russia's TASS news agency quoted North Korean Foreign Minister Ri Yong Ho as saying: "With his bellicose and insane statement at the United Nations, Trump, you can say, has lit the wick of a war against us".
(Korean Central News Agency) In this handout photo released by the South Korean Defense Ministry, South Korea's Hyunmu-2 ballistic missile is fired during an exercise aimed to counter North Korea's nuclear test on September 4, 2017 in East Coast, South Korea.
Tensions between the United States and North Korea have intensified in recent months as the Trump administration has struggled to rein in Kim Jong-un's expanding nuclear and ballistic weapons programme. While early 80 percent of the documents had not yet been identified, they reportedly included contingency plans for South Korean special forces and information on military facilities and power plants, it said.
And North Korea has denied this, and accused South Korea of "fabricating" the claims.
While US Secretary of Defense James Mattis reiterated this week that diplomacy along with worldwide economic sanctions would remain the leading element of US strategy towards blunting North Korea, military options were being prepared.