US satellite data suggests North Korea may have already begun fueling a rocket it plans to launch this month in the face of international opposition.

US satellite data suggests North Korea may have already begun fueling a rocket it plans to launch this month in the face of international opposition, a Japanese newspaper reported Friday, citing a US defense official.

Pyongyang has announced it will launch a satellite-bearing rocket sometime between February 8-25, which is around the time of the birthday on February 16 of late leader Kim Jong-Il, father of current leader Kim Jong-Un.

The North insists its space program is purely scientific in nature, but the United States and allies, including South Korea, say its rocket launches are aimed at developing an inter-continental ballistic missile capable of striking the US mainland.

North Korea "will finish preparations for the launch as soon as the next several days", the unidentified US Defense Department official told the Asahi Shimbun.

Since Thursday, satellite images have shown increased movement of people and equipment around the launch pad and a fuel storehouse at North Korea's Sohae satellite launch complex in the country's northwest, the official said, according to the Washington-datelined report.

The United States judged that fueling appears to have started as it has been monitoring Pyongyang's movements via military intelligence satellites which can analyze objects as small as 30 centimeters (12 inches), the official was quoted as saying.

Given the difficulty in stopping the process once fueling begins, preparation work normally finishes within several days of that, the official told the Asahi.

UN sanctions prohibit North Korea from any use of ballistic missile technology, and the imminent launch would amount to another major violation of UN Security Council resolutions following Pyongyang's fourth nuclear test last month.