Seoul: New satellite images of a North Korean rocket launch site show a mobile radar trailer and rows of what appear to be empty fuel and oxidiser tanks, evidence of ramped-up preparation for what Washington calls a cover for a long-range missile test.

An analysis of images provided to The Associated Press by the US-Korea Institute at Johns Hopkins School of Advanced International Studies shows Pyongyang "has undertaken more extensive preparations for its planned April rocket launch than previously understood." The images were taken Wednesday.

A mobile radar trailer essential for any launch stands at the end of a new dirt road running from the entrance of the Tongchang-ri site; it has a dish antenna that's probably a radar tracking system, according to the institute's analysis.

Radar tracking during a launch gives engineers crucial real-time information on the performance of the rocket's engines, guidance system and other details.

"These pictures are new and important evidence that the North's preparations for its rocket launch are progressing according to schedule," said Joel Wit, visiting fellow at the institute and editor of its website on North Korea, "38 North." The images are from Digital Globe, a commercial satellite photography company.

North Korea says the launch, set for sometime between April 12 and 16, will fire a satellite into orbit to study the country's crops and natural resources. It is also meant to honour one of the country's most important days the centennial of the April 15 birth of national founder Kim Il Sung.