The top U.S. military commander in the Pacific says he’s concerned by what he sees as increasing cooperation between Chinese and Russian military forces in the region.

Adm. John Aquilino, head of U.S. Indo-Pacific Command on Oahu, made the remarks Tuesday at the annual Aspen Security Forum in Colorado, saying that when it comes to Russia and China in the Pacific, “their exercises have increased, their operations have increased. I only see the cooperation getting stronger and, boy, that’s concerning, that’s a dangerous world.”

Last year Chinese leader Xi Jinping and Russian leader Vladimir Putin announced that the two countries had agreed to a “no limits partnership” to cooperate militarily in an effort to advance their interests and challenge the United States.

Aquilino said he wasn’t sure how far the new agreement goes but that “we’ve seen a lot of things that lead us to believe that it’s truly real, despite their long historical and cultural differences.”

Over the years Russian spy ships have regularly lingered off Kauai to monitor missile tests at the Navy’s Pacific Missile Range Facility, and Chinese surveillance ships routinely monitor the biennial exercise Rim of the Pacific from afar. In 2021 dozens of warships and planes from Russia’s Pacific fleet sailed just off the Hawaiian Islands to conduct what Russian officials described as the largest exercise its navy has conducted in the Pacific since the end of the Cold War.

But Chinese and Russian forces have increasingly been seen traveling together, with joint naval formations reported around Japan and the U.S.-claimed Aleutian Islands in the northern Pacific.

Aquilino noted that in June, Chinese and Russian bombers flew together toward the Philippine Sea in the direction of Guam. According to the Chinese state-run Global Times, the 22 bombers “flew beyond the range of Japanese monitoring after they entered deep into the West Pacific in the approximate direction of Guam.”

“Today, a Russian and Chinese maritime task force is doing a combined patrol,” Aquilino continued. “We’ll see where that ends up, whether it’s off the Aleutian Islands, whether it’s in the Philippine Sea, whether it goes to Guam, whether it goes to Hawaii or whether it goes off the West Coast of the United States.”

The joint maneuvers, which so far have stayed in international waters and airspace, are perfectly legal. The U.S. and its allies also regularly sailed near Chinese and Russian territory. But China has accused the U.S. military and vessels from neighboring countries of trespassing in its waters.

Beijing claims nearly the entire South China Sea, a critical waterway that more than a third of all trade travels through, as its exclusive sovereign territory. Chinese forces have built bases in disputed regions to assert those claims, and have occasionally attacked fishermen and other maritime workers from neighboring countries.

In 2016 an international court ruled in favor of the Philippines in arbitration with China, finding Beijing had violated Manila’s territorial rights. Chinese officials condemned the ruling as “illegal” and doubled down on Beijing’s territorial claims. Chinese forces have continued to intimidate fishermen in waters the Philippines claims.

“The international court (Permanent Court of Arbitration) determined China had no valid claim,” Aquilino said. “Yet they continue to threaten the Philippines. They have discounted the international ruling based on no fact other than they don’t like the decision.”

But the Chinese military’s chief concern is Taiwan. In June, Pearl Harbor-based destroyer USS Chung-Hoon had a confrontation with a Chinese navy vessel as the American ship was moving through the Taiwan Strait as part of a so-called freedom of navigation operation. Beijing considers Taiwan, a self-ruled democracy, to be a rogue province, and Xi has vowed to bring it under Chinese control.

The island is a major trade partner for the U.S. and a key provider of semiconductors that many American companies depend on to make their products work.

The U.S. has not officially diplomatically recognized Taiwan since normalizing relations with the People’s Republic of China in 1979, but the Taiwan Relations Act of 1979 maintained de facto ties and requires the U.S. to provide Taiwan with weapons “of a defensive nature” and “resist any resort to force or other forms of coercion that would jeopardize the security, or the social or economic system, of the people on Taiwan.”

“(Xi) has given the challenge to the Chinese military to be prepared, if required, to take Taiwan by force by 2027,” Aquilino said. “Those were his words, not ours. Now, my job is to prevent that conflict and we do that and work each and every day in order to prevent conflict. That said, if we think he’s set his sight to be ready by 2027, I have that mission today. We need to be ready today. And we need to get our forces in place.”

American relations with China and Russia have deteriorated sharply. The Russian and Chinese navies have attended RIMPAC in Hawaii over the past decade in hopes of promoting cooperation and friendly ties. But Aquilino said those efforts haven’t yielded results and the hopeful mood from those days has largely passed.

“That’s not the world we live in,” he said. “So to be prepared and ready to live in that world, we ought to put all of our capabilities in place, our posture initiatives in place, our alliances and partnerships in place, and we ought to do that fast.”

U.S. officials have been visiting China in recent months in hopes of cooling tensions. But top-level military communications between the two countries are currently almost nonexistent. Aquilino said he has reached out to Chinese military officials to try to restart dialogues, but so far those requests have been either ignored or refused throughout his time commanding U.S. forces in the Pacific.

He said he most recently invited senior Chinese leaders to attend INDOPACOM’s annual Chiefs of Defense Conference in Fiji next month but has heard no response.