North Korea is ramping up activity at a possible rocket launch site in preparation for what the U.S. suspects is a planned long-range missile test, satellite photographs show.

The satellite photos appear to show a mobile radar trailer, and rows of empty fuel oxidizer trucks according to the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies, the Associated Press reported.

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 tanks were apparently dumped in these locations after their contents were transferred to buildings that will directly fuel the first stage of the Unha-3.

The large number of apparently empty tanks indicates that the transfer process may have been close to completion.

AP acquired the images from commercial satellite photography company Digital Globe.

The analysis comes after North Korea accused the U.S. of breaking a bilateral nuclear disarmament deal on Saturday, saying Washington had over-reacted to its planned satellite launch in mid-April, according to an Agence France Presse report. In February, North Korea said it would suspend its nuclear activities in exchange for food aid from the U.S. That agreement is now in peril -- according to the terms of a pact between North Korea and the U.S., any such launch would result in Washington halting vital food aid to the impoverished country.

The U.S. overreaction to DPRK (North Korea's) plan... has gone beyond the limit, a foreign ministry spokesman said.

Pyongyang has repeatedly denied that what it calls a satellite launch is in fact a cover for a long-range missile test. The mid-April launch is expected to coincide with the 100th anniversary of the birth of North Korea's founder Kim Il-Sung.

While the North has already conducted two successful nuclear tests, experts do not believe the country has mastered the technology necessary to build a nuclear warhead and mount it on a missile.

Analysts will be watching the proposed launch carefully, looking to determine if the North has perfected a multi-stage rocket capable hitting the U.S. or not.