US Navy ships are being moved into position to track a North Korean rocket due to launch later this month.
North Korea plans to launch the rocket between 10 - 22 December, saying it will put a satellite into space.
The United States and other nations say the launch constitutes a test of long-range missile technology banned under United Nations resolutions.
Meanwhile, Japan has formally issued an order to its military to shoot down any rocket debris that falls on its territory.
The Kyodo news agency said three Japanese warships equipped with missile interceptors are being deployed and PAC-3 missile interceptors are also being positioned on the ground at four locations in Okinawa prefecture.
North Korea conducted a similar launch in April 2012, but the rocket flew only a short distance before crashing into waters off the Korean peninsula.
The BBC reports the launch window includes two key dates: 17 December marks the first anniversary of the death of North Korean leader Kim Jong-il and 19 December is when a presidential election takes place in South Korea.
The Yonhap news agency reports that all three stages of the rocket are now in place at the launch site and that fuel is being injected into a storage tank, after which the rocket will be fuelled.