Research has been released on the 67th anniversary of the attack on the key naval base which forced America to join World War II.

There have long been allegations that some in Washington knew in advance that the Japanese planned to target Pearl Harbor on December 7, 1941.

Now, a team at the National Security Agency (NSA) has carried out a study which rules out the long-held theory surrounding one of the Second World War's most enduring mysteries

According to historians, secret messages buried in Japanese-language weather reports, meant to alert Japanese diplomats worldwide to destroy confidential codes as war with America, Russia and Britain was beginning, did not reach US officials prior to the attack.

Under Japan's "winds execute plan", East wind rain meant the US, north wind cloudy was the erstwhile Soviet Union and west wind clear was Britain if diplomatic relations were "in danger" with one of three countries.

Washington also missed potential warning signs because intelligence resources had been diverted to the Atlantic.

The Japanese misled the US about the whereabouts of Tokyo's naval strike force, Robert J Hanyok, one of the study's authors, said.

"The problem with the conspiracy theory is it diverted attention from the real substantive problems, the major issue being the intelligence system was so bureaucratised," Hanyok was quoted as saying.

Nearly 2,400 Americans were killed and almost 1,180 injured when Japanese fighters bombed and sank 12 naval vessels and heavily damaged nine others.