North Korea may have moved the first stage of a rocket to a launch stand, indicating it is on schedule for a controversial mid-April launch, according to an analysis of satellite images.

The rocket is not visible at the Tongchang-ri site, but an analysis provided to the Associated Press by the US-Korea Institute at Johns Hopkins School of Advanced International Studies claims evidence suggests the first stage may be in the launch stand's closed gantry ahead of the planned launch on April 12-16.

The evidence, contained in satellite photos taken on Wednesday, suggests the completion of fuelling activity, with most of the empty fuel and oxidizer tanks removed from buildings supplying the first stage, a new barricade for vehicles on the road to the pad indicating higher security, and the removal of objects near the gantry and a clean-up of the launch pad.

"If past launches are any guide, at least the first stage would have to be present at the gantry if the North Koreans are going to keep to the timetable for the scheduled launch," said Joel Wit, visiting fellow at the institute and editor of its website on North Korea, 38 North.

The North Korean launch is intended to showcase national power and technology during celebrations of one of the country's most important days – the centennial of the 15 April birth of national founder Kim Il-sung. North Korea says the rocket will carry a satellite into orbit to study crops and natural resources.

Washington believes the launch is a cover to test missile systems that could target parts of the US. While North Korea has conducted two nuclear tests, analysts don't believe it has yet mastered the technology needed to mount a nuclear weapon on to a missile.

Launch preparation can also be seen in separate GeoEye satellite images from Saturday reviewed by Allison Puccioni, image analyst at IHS Jane's Defense Weekly. The pictures show vehicles on the launch pad, nearby fuel and oxidizer containers and a crane above the launch tower placed "directly over the mobile launch platform, the position necessary to erect the rocket".

Cloudy skies from Sunday until Tuesday obscured the launch site, but the US-Korea Institute's analysis says that if Pyongyang is following a timeline similar to previous launches in 2006 and 2009, workers should have put the rocket's first stage on the launch stand on Sunday or Monday, with the second and third stages coming during the next two days.

Any launch would likely destroy a 29 February accord between North Korea and the US that would ship food aid to the impoverished country in exchange for a moratorium on missile and nuclear tests, as well as a suspension of nuclear work at its main Yongbyon nuclear facility. The US says plans to provide food to the north are already on hold.

North Korea has conducted three such launches since 1998. The last, in 2009, led to UN condemnation and the north walking away from six-nation nuclear disarmament talks. Pyongyang carried out its second nuclear test weeks later.