A dozen other US allies are already taking part in the Joint Strike Fighter programme including Australia, Britain, Canada, Denmark, Italy, the Netherlands, Singapore and Turkey.

The US government has appointed defence contractor Lockheed Martin to build the F35, which will be a supersonic, multiple-role warplane.

Prime Minister Junichiro Koizumi's cabinet, the Defence Agency and the trade ministry will hold further talks over Japan's participation in the programme before seeking approval of the ruling coalition, the Sankei Shimbun said, quoting a defence industry source.

"It is now difficult for a single country to be engaged in such development," the unnamed source told the newspaper.

A Defence Agency spokesman, however, told AFP the government has not "officially begun consideration of such international military development."

Japan cleared the way for such projects by establishing new defence guidelines this month that said the country needed "multi-function, flexible defense capabilities" to deal with new threats such as terrorist and missile attacks.

The guidelines ended Japan's self-imposed ban on weapons exports, saying Tokyo could sell missile components to the United States, with other military sales to be reviewed on a case by case basis.

A press report on Wednesday said Japan was considering exporting decommissioned destroyers to Singapore and Malaysia.

The constitution imposed by US occupiers after World War II said Japan would forever renounce war. Koizumi's government has eyed revising Japan's official pacifism and sent troops on a reconstruction mission to Iraq.

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