A new satellite image shows a marked increase in activity at a missile launch site of the Democratic People's Republic of Korea, pointing to a possible long-range ballistic missile test by Pyongyang in the next three weeks.

The imagery taken by satellite operator DigitalGlobe Inc was released days after Japanese newspaper Asahi Shimbun reported that US intelligence analysts had detected moves that were seen as preparation by the DPRK for a long-range missile launch as early as this month.

DigitalGlobe, which provides commercial satellite imagery to the US government and foreign governments, on Monday released the image that it said was at the DPRK's Sohae Satellite Launch Station.

It said the imagery showed more people, trucks and other equipment at the site, a level of activity that was consistent with preparations seen before Pyongyang's failed April 13 rocket launch.

A Pentagon spokeswoman declined to comment on the reported satellite images, but said the US Defense Department's position on the DPRK's missile development efforts had not changed.

Meanwhile, Chinese Vice-Foreign Minister Zhang Zhijun held talks with his Republic of Korea counterpart Ahn Ho-young for the 5th China-ROK High-Level Strategic Dialogue in Beijing on Monday.

"The two sides reaffirmed the DPRK's denuclearization as well as peace and stability on the Korean Peninsula as their common strategic goal," the ROK Ministry of Foreign Affairs and Trade said in a news release.

Zhang Liangui, an expert on Korean Studies at Party School of Central Committee of Communist Party of China, said the conclusions of the US and Japan were based on certain proofs, and Pyongyang should take a safe and sound pace on the rocket issue.

"If Pyongyong chose the current timing to launch a satellite as a push for its ballistic missile technologies, that may prompt Washington and Beijing to turn to policies more unfavorable for Pyongyang," Zhang warned.

The ROK is gearing up for a presidential election on Dec 19 while Japan will hold its general election on Dec 16.