Describing the scandal, Taro Aso, the Japanese foreign minister, said: "They approached him, offering to arrange a sexy woman for him."
"Then he was blackmailed to give away secret codes for classified information. It is clear from a suicide note he left."
Aso said the Japanese consular official killed himself in May 2004 after having an affair with an unidentified woman.
The Foreign Ministry said there was no sign the official leaked information.
The Kyodo news agency reported that Aso planned to take action against China over the incident, but did not elaborate.
The Foreign Ministry had previously said that the official's death was a result of an unspecified diplomatic incident with a Chinese intelligence official.
"They approached him, offering to arrange a sexy woman for him"
Taro Aso, Japanese foreign minister
Aso said the diplomat was asked to provide numbers needed to decipher secret codes, but that he chose to kill himself instead because he could not sell out his country.
The government has since ordered changes to codes securing classified information and communication systems at Japanese embassies and consulates around the world.
The incident prompted Japan last month to accuse China of violating the Vienna Convention on diplomatic relations that guarantees the inviolability of diplomats.
Beijing responded by issuing a protest over Tokyo's suggestion that the actions of a Chinese spy might have forced the consular official to commit suicide.
The foreign ministry also urged embassy and consulate workers worldwide to be on their guard, and ordered all staff in China to use extra caution against potential spy activities.
"Most diplomats aren't so good looking (and) they should be trained to be cautious when they're approached by women," Aso was quoted as saying.
Amid media speculation about intelligence operations featuring "honey traps" targeting Japanese diplomats in China, Jonichiro Koizumi, the Japanese prime minister, last month warned diplomats of "seductions or attempts to steal secrets."
Relations between Tokyo and Beijing have been strained in recent months by a string of disputes.
The two sides have argued over Koizumi's visits to a shrine that honours Japan's war dead including convicted war criminals, conflicting interpretations of Japan's wartime atrocities, as well as undersea gas deposits in the East China Sea.