By Tim Kelly
TOKYO (Reuters) - Prime Minister Shinzo Abe's decision to let Japan's military fight overseas could open the way for the country to deploy minesweepers in South Korean waters in the event of a war with North Korea, a senior U.S. admiral said on Friday.
Japan's military has defined its role as purely defensive, but Abe's cabinet in July revised the government's interpretation of the pacifist postwar constitution to allow its troops to aid a friendly country under attack.
Mine-sweeping in Korean waters would give Japan's Self-Defense Forces an expanded role in its security alliance with the United States and give Washington a welcome backstop in a region where economic growth has brought more military spending.
"When you look at the Korean peninsula and the challenges for mine warfare, especially early in a conflict, the Japanese can be a critical asset," Vice Admiral Robert Thomas, commander of the U.S. Navy's Seventh Fleet, told reporters.
Thomas, based in Yokosuka in Japan, is in charge of 80 ships, including the USS George Washington, the United States' only forward deployed aircraft carrier, making the fleet the most potent in Asia.
"Would I want to have my ally Japan help me in the Korean theater of operations, and would the (South Korean) fleet also be accepting of that? I think the answer is 'yes' on both counts," he added.
But a spokesman for Japan's defence ministry said a decision on minesweeping would depend on conditions existing at the time.
"It would depend on conditions prevailing at the time as whether mine sweeping was possible or not. We couldn't answer that question now," the spokesman said.
In Seoul, a South Korean defence ministry official said no Japanese navy vessel can enter South Korea's waters to do anything without its consent.
With little fanfare, the navies of Japan, South Korea and the United States regularly hold joint exercises, including mine-sweeping, in international waters.
Abe's historic step toward a more robust military aligns Japan's armed forces more closely with the deployment options available to militaries of other advanced nations.
Welcomed by the U.S. but criticized by China, the move also prompted concern both inside and outside Japan that Tokyo could revert to militarism.
After the change was announced, South Korea called on Japan to "behave properly in a bid to win confidence from its neighboring countries," and asked Tokyo to inform of it of any action that would affect South Korea.
With some 120 warships, Japan's Maritime Self-Defense Force is America's "most capable maritime ally," Thomas said.
While the Seventh Fleet keeps tabs on Chinese activity in the region, its top priority is the Korean theater, amid the potential for conflict with a nuclear-armed North Korea.
A likely tactic of the North in any conflict could be to mine the waters around Pusan, at the southeastern tip of the Korean peninsula, close to Japan. South Korea's second biggest city has the world's fifth-biggest seaport, handling much of South Korea's imports and exports.
During the Korean War in 1950, Chinese-backed North Korean troops pushed the South Korean and U.S.-led United Nations forces all the way to Pusan, where they managed to cling on during repeated assaults, supplied by the port.
The U.N. forces pushed back to near the 38th parallel, where military stalemate culminated in a 1953 truce that still holds.
(With additional reporting by Nobuhiro Kubo in TOKYO and Ju-min Park in SEOUL; Editing by Clarence Fernandez)