Japan's cabinet is poised to approve a landmark change in security policy, paving the way for its military to fight overseas.
Under its constitution, Japan is barred from using force to resolve conflicts except in cases of self-defence.
But a reinterpretation of the law would allow "collective self-defence" - using force to defend allies under attack.
Ruling bloc lawmakers approved the move on Tuesday morning and the cabinet is expected to follow later in the day.
Prime Minister Shinzo Abe has been pushing hard for the move, arguing Japan needs to adapt to a changing security environment in the Asia-Pacific region.
The US, with whom Japan has a decades-old security alliance, will also welcome the move, but it will anger China, with whom Japan's ties are already very strained.
The decision is also highly controversial in a nation where post-war pacifist identify is firmly entrenched.
On Sunday a man set himself on fire in central Tokyo to protest against the proposed change.
Abe endorsed the move in May, after a panel of his advisers released a report recommending changes to defence laws.
Japan adopted its pacifist constitution after its surrender in World War Two. Since then, its troops have not engaged in combat, although small numbers have taken part in UN peace-keeping operations.
ARTICLE 9, JAPANESE CONSTITUTION
The Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes... land, sea, and air forces, as well as other war potential, will never be maintained
It has long held the view that under international law, it has the right to collective self-defence, but it also believes that it cannot exercise that right because of constitutional limits.
Abe's panel recommended that - if Japan reinterpreted the constitution to allow collective self-defence - conditions be imposed to ensure the power would not be abused.
On Monday, thousands of people joined a protest in Tokyo to oppose the change.
Critics of Abe fear that this move is the first step to a more permanent revision or removal of the war-renouncing Article 9 of the constitution.
"I thought that if we don't stop the Abe government now then it won't be possible to recover," Etsuo Nakashima, 32, told Reuters news agency.
But others believe that the constitution is a post-war relic imposed on Japan by the US that restricts it from engaging in the normal activities of a modern nation.
China - with whom Japan is currently engaged in a bitter territorial dispute - says it opposes the change, accusing Japan of "remilitarising" under Abe.
Once the cabinet approves the move, legal revisions must be approved by parliament. But by reinterpreting rather than revising the constitution, Abe avoids the need for a public referendum.