The US is moving navy ships into position to track a North Korean rocket due to launch later this month.

美国将部署海军战舰以监视朝鲜本月末的火箭发射活动。

The warships were moved to achieve "the best situational awareness", the US military chief in the region said.

Japan's government, meanwhile, has formally issued an order to its military to shoot down any rocket debris that infringes（侵犯） on its territory.

North Korea plans to launch its rocket between 10 and 22 December, saying it will put a satellite into space.

The US and other nations say the launch constitutes a test of long-range missile technology banned under UN resolutions.

North Korea conducted a similar launch in April 2012, but the rocket flew only for a short time before crashing into waters off the Korean peninsula.

This 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 South Korea's presidential election takes place.

Missile interceptors

South Korea's Yonhap news agency - citing unidentified sources - 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.

But a US think-tank says preparations may not be this far advanced, citing satellite images of the launch site.

Snow had forced a temporary halt to work on 4 December, the US-Korea Institute at Johns Hopkins University said on its 38 North website, but the North Koreans still had time to complete preparations on schedule.

Based on co-ordinates provided by Pyongyang, the rocket is expected to fly south - with stages dropping into the sea west of the Korean peninsula and then east of the Philippines.

Admiral Samuel Locklear, head of US forces in the Asia-Pacific region, said preparations for the launch were being watched "very closely".

On the warships, he said it "should seem logical that we'll move them around so we have the best situational awareness".

"To the degree that those [navy] ships are capable of participating in ballistic missile defense, then we will position them to be able to do that," he said.

The rocket's flight plan also takes it close to parts of Japan's Okinawa prefecture. The Japanese government has pledged to shoot down any debris that falls over its territory.

It is deploying three warships equipped with missile interceptors and is also positioning PAC-3 missile interceptors on the ground at four locations in Okinawa prefecture, Kyodo news agency said.

All Nippon Airways, meanwhile, says it is adjusting flight plans to avoid the area off the Philippines where the second stage of the rocket may fall.

Similar preparations by the US and Japanese militaries were seen ahead of the failed launch in April. But the 30m Unha-3 rocket is thought to have flown for only minutes before breaking up.

North Korea has not yet successfully launched a three-stage rocket, despite four attempts since 1998. It is believed to be working on the development of a long-range missile capable of reaching the west coast of the US mainland.

The US and its allies say the rocket launches represent banned tests of ballistic missile technology because the basic technology is the same.