China shipped missile launch vehicles to North Korea last year in breach of U.N. resolutions, but was never rebuked because the U.S. did not want to embarrass Beijing, a Japanese newspaper said Wednesday.

The report, based on Japanese government sources, is the most strident of recent claims that China has been involved in helping to arm its wayward ally after earlier allegations Beijing supplied technology.

Four giant trucks capable of transporting and launching ballistic missiles were exported by a Chinese firm last August, the leading Asahi Shimbun said.

The vehicles were likely those on display at the huge military display in April marking the centenary of the birth of the state’s founder Kim Il Sung, the Asahi said.

The sale of weapons systems to Pyongyang is banned under U.N. Security Council resolutions aimed at containing the hermit state’s nuclear ambitions.

But at Washington’s urging, Tokyo and Seoul have avoided confronting Beijing in a bid to keep North Korea’s patron onside in the international effort to tamp down tensions on the peninsula, the paper reported.

Top government spokesman Osamu Fujimura declined to confirm the report, saying it was “a matter of intelligence”.

But he added, in general terms “if Japan obtains information about any violation of the UNSC resolution, the government will address the matter in cooperation with concerned nations.”

Japanese government papers reveal four 16-wheel vehicles were transported aboard a Cambodian-registered ship, which was tracked by spy satellites leaving Shanghai on August 1 and arriving at Nampho in western North Korea three days later, the Asahi said.

The vessel then moved on to Osaka where the Japanese coastguard conducted an on-board inspection and discovered documents detailing the export of the vehicles, issued by an agent in Shanghai, the Asahi said. (AFP)