Two U.S. Air Force bombers flew over North Korea on Tuesday night, in a demonstration aimed at deterring North Korean military activity on the 72nd anniversary of the regime's ruling party, Reuters reported. Such flights by the powerful aircraft based in Guam incense the North, which claims they are preparation for war; Pyongyang has threatened to send missiles into the waters around Guam.
Tensions between North Korea and the United States have risen in recent weeks over Pyongyang's nuclear weapons and missile programs.
Rhee told CNN on Tuesday that the documents stolen included the South Korea-US wartime operational plan and a document that includes procedures to "decapitate" the North Korean leadership.
While North Korea was not able to hack US power companies, there are concerns among some of observers that the regime may attempt to damage the power grid by detonating a nuclear device at a high altitude above the USA, triggering an electromagnetic pulse (EMP).
The warplanes first conducted a simulated air-to-ground missile drill over the waters east of the Korean Peninsula and then flew over South Korea and conducted the same drill over the waters west of the peninsula, the South Korean military said.
The two B-1B bombers were accompanied by two F-15K fighters from the South Korean military after leaving their base in Guam, the South's Joint Chiefs of Staff said in a news release.More news: New study highlights big offshore wind opportunities in North Atlantic
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".
There are also serious concerns about North Korea's cyberwarfare capabilities, but the USA has been carrying out operations of its own to counter North Korean cyber operations in Northeast Asia and elsewhere.
After Pyongyang launched a missile test that flew over Japan in late August, the state-run Korean Central News Agency said the test was "a meaningful prelude to containing Guam", which it called the "advanced base of invasion" for U.S. forces.
President Trump hosted a discussion on options to respond to any North Korean aggression, or, if necessary, to prevent Pyongyang from threatening the U.S. and its allies with nuclear weapons, the White House said in a statement.
The F-15 escorts are notable "because combined operations require consent from South Korea, so this does not represent USA unilateral action", according to Pinkston. North Korea routinely denies responsibility.