"We do not assume a situation in which we use them for the purpose of killing residents inhumanly in other countries," Shigeru Ishiba, the state minister and director general of the Defence Agency, said in parliament.

It was reported on Thursday that Japan's air force had bought thousands of cluster bombs, worth some 15 billion yen (120 million US dollars) in the past 16 years by vaguely listing them as "munitions" in budget documents.

The Defence Agency confirmed the report but did not reveal the exact number of 1,000-pound cluster bombs deployed at air bases around Japan.

International human rights groups have urged the US military to refrain from using cluster bombs, which can contain up to 3,000 bomblets, each of which explodes separately.

They also claim that US forces used these bombs in the former Yugoslavia and Afghanistan. Many cluster bombs have failed to detonate on impact, posing a danger to civilians similar to that of land mines.

Ishiba told the parliamentary committee on contingency legislation: "In case we use them in our country, we evacuate residents as a matter of course. We dispose of them in a strict and safe manner after repelling the invasion of enemies."

He said cluster bombs would be "effective in attacking the positions of invading enemies" and their depots for tanks and other vehicles and useful, if Japan were to be attacked, in "blocking the invasion."

SPACE.WIRE