North Korea has sent a fax to South Korea threatening to attack "without notice" in response to anti-Pyongyang rallies held on the second anniversary of Kim Jong Il's death earlier this week, South Korea's largest news agency reported Friday.
According to Yonhap news agency, the north's powerful National Defense Commission sent the message to South Korea's National Security Council through on Thursday.
NBC News was unable to independently verify the report.
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The North Korean military apparently condemned the rallies by several conservative groups and defectors from the isolated communist state on Tuesday, saying they insulted North Korea's "highest dignity," referring to its young leader Kim Jong Un.
Meanwhile, top Pentagon officials warned on Thursday that the execution of his uncle last week is an example of the worrisome unpredictability of that regime and could be a prelude to some kind of provocation by Pyongyang.
The execution of Jang Song Thaek was the biggest upheaval in years in North Korea, which has conducted three nuclear tests and this year raised the possibility of nuclear war with South Korea and the United States.
"These kind of internal actions by dictators are often a precursor to provocation to distract attention from what they're doing inside of that country," General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, told a Pentagon news conference.
North Korea's KCNA news agency said last week Jang had been executed for trying to seize power and for driving the economy "into an uncontrollable catastrophe."
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But North Korean politics are virtually impenetrable from outside. Analysts have speculated, for instance, that Jang could have been purged over a falling out with Kim or other personal reasons.
Defense Secretary Chuck Hagel said that uncertainty about North Korea's motives is "concerning to everyone."
—By Henry Austin. Reuters contributed to this report.