Citing threats from China and North Korea, a government-appointed panel has urged Japan to reinterpret its pacifist constitution to allow the use of military force to defend other countries.
The recommendation, submitted today to Prime Minister Shinzo Abe, sets the stage for his push to allow the military to play a greater role in international security.
Japan currently maintains a military only for its own defense, and has previously interpreted the war-renouncing Article 9 of its postwar constitution to mean it cannot engage in what is known as collective self-defence.
If approved, the change could allow Japan to come to the defense of the United States or other countries, even if Japan itself is not under attack.
Japan has gradually loosened the restrictions of Article 9 over the years to allow overseas deployments of troops in limited circumstances, but never to use their weapons to fight for others.
"Collective self-defense probably goes even further than all the other reinterpretations that Article 9 has seen thus far, so it would be a huge step," said Chris Winkler, a constitutional expert at the German Institute for Japanese Studies in Tokyo.
The proposal faces doubts within Abe's ruling coalition and he will have to build a consensus to win Cabinet approval.
Surveys show public opinion is mixed. Opponents say it would undermine the war-renouncing clause of the constitution.
"Currently, the bottom line is whether Japan comes under foreign attack," said Kyouji Yanagisawa, a security expert under former Prime Minister Junichiro Koizumi. "Then, what serves the brake for an abuse of the right to self-defense when Japan is not under direct attack?"
The report said that a deteriorating regional security environment, namely threats from China and North Korea, makes Japan's ban on collective self-defense inadequate.
The change is needed in the face of rising tensions in east Asia and pressures on US military spending, said Yosuke Isozaki, Abe's national security adviser.
"Japan will become a country that can make more international contributions by deepening its relations with the U.S. And expanding our ties with countries other than America," he said.
The United States backs Abe's push for a larger military role, as it wants Japan to bear a greater burden of its own defence.
