The United States plans to use missile defence assets to track an expected North Korean missile launch as tensions escalate over Pyongyang's plan to fire a rocket soon.
Ashton Carter, the US Secretary of Defense, however, declined to comment further on Thursday on any specific plans to position navy ships or move a large sea-based radar to the Asia Pacific region before the imminent launch.
Japan has said it put its military on alert to shoot down any rocket that threatens its territory.
North Korea notified the United Nations this week of its plan to put an "earth observation satellite" into orbit some time between February 8 and 25.
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Pyongyang says that it has a sovereign right to pursue a space programme, although the United States and other countries allege that such launches are missile tests in disguise.
Wang Yi, the Chinese foreign minister, said that Beijing sent its special envoy for the nuclear issue, Wu Dawei, to North Korea in what he described as "a serious situation".
"We don't want to see anything happen that could cause further tensions," Wang told Hong Kong's Phoenix Television in London after Wu returned from North Korea.
"We hope all sides, including North Korea, can meet each other halfway and should work hard together to push the North Korean nuclear issue on to the track of a negotiated resolution."
Yun Byung-se, the South Korean foreign minister, on Friday held a meeting with the US, Japanese, European Union and Australian ambassadors over the issue.
North Korea said that the launch would be conducted in the morning during the announced period, and it provided coordinates for the locations where the rocket boosters and cover for the payload would drop.
Those locations are expected to be in the Yellow Sea off the Korean peninsula's west coast, and in the Pacific Ocean to the east of the Philippines, Pyongyang said.
North Korea last launched a long-range rocket in December 2012, sending an object it described as a communications satellite into orbit.
Tension has risen in North Asia since Pyonyang's fourth nuclear test last month, which it said was a hydrogen bomb.
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