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(CNN) — A North Korean buildup and partial mobilization of military forces since late last week caused so much consternation at the Pentagon that top U.S. commanders reviewed the U.S. war plan for defending South Korea in case there was a sudden indication that North Korea was going to begin a war, CNN has learned.
Two U.S. officials confirmed the details of the North Korean buildup to CNN, with the U.S. now trying to assess how much of that North Korean buildup is continuing after North and South Korea reached a deal Monday in talks at the historic "truce village" inside the Demilitarized Zone.
The U.S. officials stressed that the buildup is seen as serious. The U.S. had grown increasingly worried about North Korean intentions after leader Kim Jong Un put a specific deadline on the table for South Korea to stop the propaganda broadcasts it has been blasting across the border. The broadcasts will stop as part of the fresh deal, according to the South Korean presidential office.
The buildup led to a series of urgent discussions inside the U.S. military and between the US and South Korean military about the U.S. war plan. The officials told CNN that over the last few days, U.S. commanders and military planners have reviewed the plan to ensure has been updated to include what U.S. forces are available if needed, and what actions by North Korean would trigger a U.S. military response. The U.S. has also been talking to the South Koreans to try to encourage them to deescalate the situation, the officials said.
Based on overhead satellite imagery and other intelligence gathering, the U.S. military intelligence assessment concluded that the North Koreans late last week began a limited mobilization including:
Activation of some air defense radars that might be able to detect incoming aircraft.
Deployment of additional artillery pieces near the DMZ. Officials would not offer additional details, but the concern has always been that North Korean artillery could hit population center in the South such as Seoul.
Signs of potential preparations for a short- or medium-range SCUD missile launch. The U.S. also sees unrelated signs that North Korea may be preparing for another test of its intercontinental ballistic missile sometime in the coming weeks.
Deployment of as much as one-third of the coastal surface vessel and submarine fleet.
As of Monday, some of those ships were headed back into port for resupply, one U.S. official said, because the North Korean navy is not able to resupply while ships are at sea. However the official, who follows North Korean military moves, added, "I don't like to use the word unprecedented, but we haven't seen this before from their Navy."
The U.S. is now trying to determine if the forces remain in the field, and what the North Korean intention is about maintaining that presence, given their limited financial ability to undertake large military operations.
As part of those weekend talks about U.S. military planning, the U.S. is considering canceling a potential flight of a B-52 bomber as part ongoing military exercises with South Korea out of concern it could be seen as an escalation to Pyongyang.
The Pentagon had acknowledged last week that those exercises had been temporarily paused for several hours so commanders could review the situation with North Korea, but did not disclose details of the buildup.
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