Japan's defence minister has said Tokyo may consider adopting an offensive military capacity, going against its pacifist constitution.
Security is tight for Japan's launch of its first spy satellites on Friday
Shigeru Ishiba, who is known for his hawkish views, told the House of Representatives Committee on Security that it is "worth considering" offensive capability.
He was speaking as final preparations were made for the launch on Friday of two information gathering satellites, which will be able to monitor its neighbour, North Korea.
Mr Ishiba's remarks are likely to stoke fears in North-East Asia of rising Japanese assertiveness.
Although Japan's military is one of the most modern and best equipped in the world, it is restricted under the country's constitution to defence. Its aircraft have no ground attack capability and it has no guided missiles to attack foreign military facilities.
But rising tensions with North Korea over its nuclear weapons programme have thrown into relief Japan's vulnerability.
At the committee meeting, Mr Ishiba was asked if the government planned to consider the introduction of an offensive military capability.
"It is worth considering it," he said.
"It is necessary to examine (the issue) from various points of view. If we stop considering it, we will be unable to take responsibility for the peace and independence of our country," Mr Ishiba said.
The defence chief created waves when he was reported in February as saying that Japan would consider a pre-emptive strike on North Korea, although he later backed down from such comments.
On Thursday, he repeated his support for the introduction of the US-made Patriot anti-missile system.
"If it is exclusively defence-oriented, I think there is no reason to reject it," he said.
Japan currently has short-range Patriot rockets, but is reported to be considering a longer-range version, the PatriotPAC2, which has a range of 1,000 kilometres (620 miles).
Japan was shocked when North Korea flew a long-range ballistic Taepodong missile over the country in 1998.
Intelligence reports have said that the North is preparing to test-fire another ballistic missile in retaliation for Tokyo's spy satellite launch.
The two satellites are due to be launched under tight security from the southern remote island of Tanegashima on Friday morning.
The satellites, which are expected to be in use for about five years, are to orbit earth at a height of 400-600 kilometres (250-370 miles).
They will allow Japan, which has hitherto relied on commercial satellite photos bought from the US and France, to develop more independent surveillance capability.