When it comes to territorial disputes in Asia, the South China Sea typically commands the bulk of attention. But the East China Sea, a lesser-known hotbed of tensions, might be more likely to trigger an international conflict.

“Despite the lower profile, the dispute in the East China Sea may carry greater risk of drawing the United States into conflict with China than the various disputes in the South China Sea,” Ryan Hass, David M. Rubenstein Fellow at Brooking’s foreign policy program, wrote in a note on Wednesday.

Both China and Japan lay claim to a set of islands in the East China Sea that cover around 81,000 square miles. Called Senkaku in Tokyo and Diaoyu in Beijing, the area is near major shipping routes and rich in energy reserves.

“There is greater risk of an unintended incident between Chinese and Japanese forces operating in the East China Sea,” Hass explained, citing “the frequency of close-in operations involving Chinese and Japanese assets, the absence of mature risk- reduction mechanisms, and the lack of consensus between Beijing and Tokyo on acceptable behavior.”

Japan is a close ally of the U.S so if a Chinese-Japanese conflict occurs, the world’s largest economy may have to step in given that it seeks to protect allies as well keep sea and air space open, Hass explained. If Beijing were to deny access to ships or planes which are operating in accordance with international law, that could also trigger a reaction from the White House, he added.

Former President Barack Obama was the first U.S. leader to state that the disputed East China Sea islands were covered by the U.S.-Japan Security Treaty. President Donald Trump meanwhile, has frequently criticized Beijing’s aggressive behavior in the South China Sea.

For China and Japan, “events in the East China Sea take on heightened significance because the dispute is perceived in both countries as a proxy for how they will relate to each other as Asian powers,” Hass explained. Previous flare-ups have rapidly roused public emotions, resulting in “limited political space for leaders in Beijing and Tokyo to de-escalate,” he continued.

In 2012, Tokyo’s decision to purchase three of the five disputed islands from their private owner triggered violent anti-Japanese protests in China, forcing Japanese firms to shut down businesses on the mainland. The following year, Tokyo lodged a protest following Beijing’s declaration of a formal Air Defense Identification Zone over parts of the East China Sea.

Moreover, “the frequency of close encounters between Chinese and Japanese ships and aircraft in the East China Sea is intensifying” and will likely continue as both countries look to improve their respective air and maritime capabilities in the zone, Hass noted.

Chinese vessels have repeatedly sailed near the islands in recent years, according to Japan’s Coast Guard, while Japanese fighter jets have conducted joint drills with U.S. aircrafts over the territory.

This is in contrast to the South China Sea, where matters appear to have reached a stalemate, Hass argued.

“Washington cannot force Beijing to abandon the artificial islands it has constructed or stop China from deploying military assets on them without risking a military conflict,” he said.

“By the same standard, China cannot stop the United States from operating in the area without risking a major conflict that would expose Chinese forces to significant risk of defeat and potentially result in the rapid destruction of its artificial islands.”

Research last week revealed Beijing has built several new facilities around the Spratly and Paracel islands recently.

In addition, the threat of conflict in the resource-rich zone is mitigated since “risk-mitigation measures are more mature” than the East China Sea, Hass pointed out, noting that Washington and Beijing have protocols to prevent unsafe encounters. Japan and China, meanwhile, only just agreed to set up a communication mechanism to prevent clashes in the East China Sea, Kyodo News agency reported earlier this month.