Media playback is unsupported on your device Media caption In April 2012, the BBC's Damian Grammaticas was invited by North Korean officials to witness preparations for the launch

North Korea has moved into place a long-range rocket for a controversial launch later this month - amid reports it is also planning a nuclear test.

Pyongyang says the Unha-3 rocket, which it plans to launch between 12 and 16 April, will put a satellite into orbit.

But opponents of the move fear it is a disguised long-range missile test.

Meanwhile, South Korean officials say new satellite images suggest the North is preparing to carry out a third nuclear test.

The images show piles of earth and sand at the entrance of a tunnel at the Punggye-ri site, where tests of a nuclear bomb were previously carried out in 2006 and 2009, South Korea's Yonhap news agency reports.

"Recent satellite images led us to conclude the North has been secretly digging a new underground tunnel in the nuclear test site... besides two others where the previous tests were conducted," one unnamed official told the AFP news agency.

North Korea has been under close scrutiny by its neighbours and the international community since Kim Jong-un became leader of the secretive state following the death of his father, Kim Jong-il, in December 2011.

At the scene Hidden behind a fold in the hills, on North Korea's coastline, its Unha rocket looked almost ready for launch. Painted with the North Korean flag, it towered 30m high. Soldiers stood guard while technicians worked on the rocket. It is a birthday present for the North's former dictator Kim Il-sung, designed to put a satellite into polar orbit, to mark his 100th birthday, even though he died 17 years ago. North Korea wants to convince its own people that their nation is now strong and prosperous.

Pyongyang had agreed in February to a partial freeze in nuclear activities and a missile test moratorium in return for US food aid. But the deal was put on hold last month after the North announced its rocket launch plans.

'Peaceful purposes'

The BBC's Damian Grammaticas was among a group of foreign journalists taken by train to the Sohae satellite station at Tongchang-ri, on the country's north-west coast, on Sunday to see the final preparations for the rocket launch.

All three stages of the rocket were visibly in position at the launch pad.

Station manager Jang Myong-jim told reporters that preparations were on track and fuelling would begin soon, without giving exact timings.

He said the 100kg (220 pound) satellite is designed to send back images and information that will be used for weather forecasts as well as surveys of North Korea's natural resources.

But should the country be putting its effort into a satellite launch when it cannot feed its own people, our correspondent asked.

''If we don't develop our own technology, we will become slaves,'' the director of the launch site told the BBC. ''We need our own technology to be an advanced country, to be a powerful space nation.''

Pyongyang has previously said the launch, for "peaceful purposes", is to mark the centennial of the birth of founding leader Kim Il-sung.

But the United States and North Korea's neighbours say it contravenes UN resolutions that were imposed after a similar launch in April 2009.

Japan and South Korea have warned they will shoot the rocket down if it strays into their territory.

The North says any of those responses would be considered hostile acts. But it seems determined to go ahead even if it sets off a dangerous cascade of events, says our correspondent.