Information on military aircraft and nuclear power plants may have been stolen in a series of cyberattacks on Japanese defence contractor Mitsubishi Heavy, a report said Monday.

Mitsubishi Heavy said late last month that 83 computers at 11 of its facilities had been hit by cyberattacks but no leakage of information on products and technologies had been confirmed.

The Asahi Shimbun newspaper reported that additional checks on other computers at Mitsubish Heavy facilities had shown traces of transmissions of information through some of the computers.

The daily, quoting unidentified officials, said part of the information concerned fighters and helicopters that the company is contracted to manufacture for the defence ministry.

"It is not known if these are classified as defence secrets," Asahi said.

Other pieces of information taken are likely to include the design, equipment and earthquake-resistant nature of nuclear power plants in which Mitsubishi Heavy was involved, the daily said.

Mitsubishi Heavy's public relations office said it could not confirm or deny the report.

Defence minister Yasuo Ichikawa said in September there was no indication that sensitive information had been stolen as a result of the attacks on the firm's computers, which came to light in August.