TOKYO—Japanese Prime Minister Shinzo Abe took a significant step toward removing six-decade-old constraints on Japan's military, a move that could enable Tokyo to play a greater security role in an increasingly tense East Asia.
Citing the recent standoff in disputed South China Sea waters between China and Vietnam, Mr. Abe said Japan needed more freedom of action in overseas conflicts, despite its pacifist constitution.
"In the South China Sea, even as we speak, confrontations between countries are continuing because of unilateral action backed by force," he said at a news conference Thursday. "It could very well be our problem."
Mr. Abe said his government would kick off discussions to determine whether to change the interpretation of the constitution to permit the use of "collective self-defense." The shift would allow Japanese troops, known as the Self-Defense Forces, to aid its allies even if Japan itself isn't attacked.
To illustrate the need for collective self-defense, Mr. Abe pointed to a panel depicting a U.S. ship carrying Japanese children being attacked by an unidentified continental country west of Japan labeled "the aggressor." In such a scenario, he said, the government couldn't send forces to help the children—unless it changed a policy that dates to the founding of Japan's modern military in the early 1950s.
Leaders of the New Komeito Party, a junior partner in the ruling coalition led by Mr. Abe's Liberal Democratic Party, have expressed caution over the change. They say Japan's 1947 constitution, written by U.S. authorities during the postwar occupation, already permits Japanese forces to come to America's aid even without the concept of collective self-defense.
"Lifting the limits on the right for self-defense will bring us right back to the concept before the last war that led us to destruction," said Katsumasa Suzuki, an opposition lawmaker, earlier this year.
Separately, China, which was invaded by Japan in the 1930s, has warned about what it calls a return of Japanese militarism. Beijing says the U.S.-Japan alliance is improperly targeting China. Mr. Abe said Japan would never wage an aggressive war and called his moves a way to ensure peace.
China's Foreign Ministry said the country was wary about changes in Tokyo's defense policy owing to "historical issues"—a reference to the invasion and occupation beginning in the 1930s.
"Due to various negative directions on historical issues that have been arising in Japan, Asian countries, including China, and the international community, have full reason to be highly vigilant over Japan's true intention and its future development," Chinese Foreign Ministry spokeswoman Hua Chunying said at a daily briefing in Beijing.
South Korea said it would keep a close watch on Japan's proposed constitutional reform.
"The South Korean government once again stresses that defense and security-related discussions in Japan must take place in a way that uphold the spirit of Japan's pacifist constitution, maintains transparency and contributes to stability and peace in the region," South Korean Foreign Ministry spokesman Cho Tai-young said in a statement.
The escalating tensions in the South China Sea, where Vietnam is trying to force China to remove a large oil platform, have fueled worries in Japan about its own territorial feud with Beijing involving a group of East China Sea islands.
Before Mr. Abe spoke to the nation, a government advisory panel recommended allowing Japan's military to aid the defense of "foreign nations with close relationships" in certain circumstances. The panel cited threats from China and North Korea.
Japan's constitution renounces the "right of belligerency." Many in Mr. Abe's ruling conservative party have long called for it to be rewritten, but that requires the support of two-thirds of parliament and a majority of the public. The panel endorsed a reinterpretation, which Mr. Abe could do on his own.
Once a cabinet decision on collective self-defense is made—which officials say they hope to complete by late summer—Tokyo plans to implement by the end of the year a cascade of changes to its defense-related laws to reflect the new interpretation.
Japanese officials say lifting the ban on collective self-defense is mainly aimed at equalizing the alliance with the U.S., which requires U.S. forces to defend Japan if it is attacked but not necessarily vice versa.
Mr. Abe's move could also pave the way for Tokyo to work more closely with regional allies such as Australia and India and members of the Association of Southeast Asian Nations such as the Philippines and Vietnam. The latter two are seeking to counter China's growing military presence.
"I would like to see Japan say to the Asean countries, 'We want to support you. How can we empower these countries?' " said former U.S. Deputy Secretary of State James Steinberg, who now teaches at Syracuse University, during a visit to Tokyo this week.
Since taking office in late 2012, Mr. Abe has made significant efforts to strengthen Japan's security ties with "like-minded nations" in the western Pacific to counter China's rapid military buildup. Responding to a request from Hanoi, Japan in March said it would consider giving Vietnam patrol ships. A Japanese Foreign Ministry official said the timing hasn't been decided but the current South China Sea conflict could accelerate the plans.
"Actively establishing close ties with Southeast Asian nations allows Japan to become a full-fledged member of the security partnership for the entire region," said Narushige Michishita, professor of strategic studies at the National Graduate Institute for Policy Studies.
