Following North Korea's long-range rocket launch on Sunday, South Korean and US military officials announced they would begin formal discussions on placing the Terminal High Altitude Area Defense System (THAAD) on the North's doorstep.
"Without getting into a timeline, we'd like to see this move as quickly as possible," Pentagon spokesman Peter Cook said.
"We are beginning the consultations now and in the current days with the South Koreans, and we expect that this will move in an expeditious fashion."
The highly deployable THAAD system fires anti-ballistic missiles into the sky to hit enemy missiles either inside or outside the Earth's atmosphere during their final flight phase.
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China firmly opposes the deployment of the anti-missile hardware so close to its borders, but Cook said the THAAD system was in no way meant to pose a threat to the Asian giant.
"If the THAAD system were deployed to the Korean Peninsula, it would be focused solely on North Korea, contribute to a layered missile defense that would enhance the alliance's existing missile-defense capabilities against potential North Korean missile threats," he said.
"Once... Decisions are made, that (timeframe) is possible," the official said, speaking on condition of anonymity.