Yesterday, when we discussed the NYT's report that the Obama administration had been waging a cyberwar against North Korea's missiles for at least three years, leading to frequent "unexplained" crashes just on or following launch, we concluded with a cautionary question "whether Kim Jong-Un, already facing a potential mutiny at home (to which he has so far responded by demonstratively executing official with anti-aircraft guns) will take this confirmation of what many would call an act of war by the US, and retaliate."

It now appears that Kim is doing precisely that when North Korea on Monday fired "several" banned ballistic missiles that flew about 1,000 kilometers (620 miles) into waters off its east coast, South Korea's military said, an apparent reaction to huge military drills by Washington and Seoul that Pyongyang insists are an invasion rehearsal. Japan has since noted that of the four missiles, three landed in its exclusive economic zone, with cabinet chief Suga warning that the launch is a "grave threat" to Japan's security, adding that Japan cann not tolerate North Korea's provocative actions. Meanwhile, Japan's prime minister has lodged a "strong protest" to North Korea.

It was not immediately clear what type of missile was fired or the exact number; Pyongyang has staged a series of missile test-launches of various ranges in recent months. The ramped-up tests come as leader Kim Jong Un pushes for a nuclear and missile program that can deter what he calls U.S. and South Korean hostility toward the North.

Seoul and Washington call their military drills on the Korean Peninsula, which remains in a technical state of war because the 1950-53 Korean War ended with an armistice and not a peace treaty, defensive and routine.

As AP adds, the South's Joint Chief of Staff said in a statement that Monday's launches were made from the Tongchang-ri area in North Pyongan province. The area is the home of the North's Seohae Satellite Station where it has conducted prohibited long-range rocket launches in recent years.

The North hates the military drills, which run until late April and which analysts say force its impoverished military to respond with expensive deployments and drills of their own. An unidentified spokesman for the North's General Staff of the Korean People's Army said last week that Pyongyang's reaction to the southern drills would be the toughest ever but didn't elaborate. North Korea test-launched a new intermediate-range missile in February and conducted two nuclear tests last year. There has also been widespread worry that the North will conduct an ICBM test that, when perfected, could in theory reach U.S. shores. Washington would consider such a capability a major threat.

The United States has 28,500 troops stationed in South Korea as a deterrent against a potential aggression from the North.

So far the Obama administration has not announced what, if any, response it would take to the latest launch.