TOKYO—Japan’s military may join U.S. forces in conducting regular patrols in the South China Sea, according to the nation’s top uniformed officer, underscoring how China’s territorial claims are encouraging Tokyo to play a greater role in regional security.

Adm. Katsutoshi Kawano, chief of the Joint Staff of the Japan Self-Defense Forces, said in an interview that China’s recent moves to build artificial islands have created “very serious potential concerns” for Japan, a trading nation that relies on the sea lane that runs through the area.

“Of course, the area is of the utmost importance for Japanese security,” Adm. Kawano said. “We don’t have any plans to conduct surveillance in the South China Sea currently but depending on the situation, I think there is a chance we could consider doing so.”

Adm. Kawano didn’t specify what actions by China might trigger Japanese consideration of patrols, and any activity by Japan’s military beyond its borders would likely raise concerns at home.

However, Japan’s participation would be a welcome move for the U.S., which has sought to rely more on allies to provide peacekeeping in the region. “I view the South China Sea as international water, not territorial water of any country, and so Japan is welcome to conduct operations on the high seas as Japan sees fit,” said Adm. Harry Harris, head of the U.S. Pacific Command, at a briefing in Tokyo earlier this month.

Troops from Japan’s navy have been conducting joint drills this week with the Philippine navy around Palawan Island, just a few hundred kilometers from the Spratly Islands, which are at the heart of a territorial dispute between Beijing and Manila. The session features Japan’s P-3C surveillance aircraft, which Adm. Kawano described as having “a superb ability for detecting submarines and other objects in the water.”

The U.S. has pledged to send aircraft and naval ships to contest China’s claims, and Australia already runs military patrols.

Adm. Kawano took the helm of the military late last year as Prime Minister Shinzo Abe was seeking to ease decades-old self-imposed restrictions on the nation’s Self-Defense Forces. Mr. Abe has cited China’s military buildup and North Korea’s nuclear-weapons development for the shift.

“In the case of China, as we can see with the South China Sea problem, they are rapidly expanding their naval presence and their defense spending is still growing,” Adm. Kawano said. “Also because there is a lack of transparency, we are very concerned about China’s actions.”

Asked about Adm. Kawano’s comments, a Chinese Defense Ministry spokesman said China’s construction activities in the Spratly Islands “are entirely a matter within our sovereignty, which is beyond reproach.” The spokesman said countries outside the region shouldn’t try to raise tensions with military intervention “which will only cause an adverse impact.”

In April, Japan and the U.S. revised the guidelines for their defense cooperation for the first time in 18 years, allowing Japan to contribute more to peacekeeping in Asia. Mr. Abe now must pass a set of bills to change domestic laws governing his pacifist nation’s military, a challenge given the caution expressed by lawmakers even within his own coalition.

Adm. Kawano said he hoped to see more military cooperation with South Korea, an area that has suffered because of disagreements between Tokyo and Seoul over wartime history. A sign of a thaw came this week when leaders of both nations attended events marking the 50th anniversary of normalizing diplomatic relations.

“Once the relations are normalized on political levels, I believe movements will emerge on our levels,” Adm. Kawano said.

He said Japan would also like to conduct more joint exercises with Australia and India. “I believe the Japan Self-Defense Forces boast an extremely high level of proficiency,” Adm. Kawano said. “We can have a positive impact on other militaries.”

He praised closer ties with the U.S. Japan’s navy now has an officer stationed at the Office of the Chief of Naval Operations at the Pentagon. “The alliance with the U.S. is our foundation. That’s how we build deterrence,” he said.

—Olivia Geng contributed to this article.