U.S. Gen. Mark Milley, chairman of the Joint Chiefs of Staff, said the number of intercepts by Chinese aircraft and ships in the Pacific region with U.S. and other partner forces has increased significantly over that time, and the number of unsafe interactions has risen by similar proportions.

“The message is the Chinese military, in the air and at sea, have become significantly more and noticeably more aggressive in this particular region,” said Milley, who recently asked his staff to compile details about interactions between China and the U.S. and others in the region.

His comments came as the U.S. redoubles efforts to strengthen its relationships with Pacific nations as a counterbalance to China, which is trying to expand its presence and influence in the region. The Biden administration considers China its “pacing threat” and America’s primary long-term security challenge.

Milley’s trip to the region is sharply focused on the China threat. He will attend a meeting of Indo-Pacific chiefs of defense this coming week in Australia, where key topics will be China’s escalating military growth and the need to maintain a free, open and peaceful Pacific.

U.S. military officials have also raised alarms about the possibility that China could invade Taiwan, the democratic, self-ruled island that Beijing views as a breakaway province. China has stepped up its military provocations against Taiwan as it looks to intimidate it into unifying with the communist mainland.

U.S. military officials have said Beijing wants to be ready to make a move on the island by 2027. The U.S. remains Taiwan’s chief ally and supplier of defense weapons. U.S. law requires the government to treat all threats to the island as matters of “grave concern,” but remains ambiguous on whether the U.S. military would defend Taiwan if it were attacked by China.

China’s joint chiefs of staff chairman, Gen. Li Zuocheng, told Milley in a call earlier this month that Beijing had “no room for compromise” on issues such as Taiwan. He said he told Milley that the U.S. must “cease U.S.-Taiwan military collusion and avoid impacting China-U.S. ties and stability in the Taiwan Strait.”

The U.S. and others are also worried that a recent security agreement that Beijing signed in April with the Solomon Islands could lead to the establishment of a Chinese naval base in the South Pacific. The U.S. and Australia have told the Solomon Islands that hosting a Chinese military base would not be tolerated.

“This is an area in which China is trying to do outreach for their own purposes. And again, this is concerning because China is not doing it just for benign reasons,” Milley told reporters traveling with him. “They’re trying to expand their influence throughout the region. And that has potential consequences that are not necessarily favorable to our allies and partners in the region.”

Milley’s visit to Indonesia is the first by a U.S. joint chiefs chairman since Adm. Mike Mullen in 2008. But U.S. leaders have crisscrossed the Asia-Pacific in recent months, including high-profile visits by Defense Secretary Lloyd Austin and Secretary of State Antony Blinken.

The Biden administration has been taking steps to expand its military and security relationship with Indo-Pacific nations as part of a campaign to build a stronger network of alliances in China’s backyard and counter China’s growing influence.

Milley declined to provide specific numbers of unsafe Chinese interactions with U.S. and allied aircraft and ships. But Austin, in a speech in Singapore last month, referred to an “alarming increase” in the number of unsafe intercepts by People’s Liberation Army aircraft and vessels.

Austin specifically pointed to a February incident where a PLA navy ship directed a laser at an Australian P-8 maritime patrol aircraft. But there have been a number of others. A surveillance aircraft controlled by Canada was recently intercepted by a Chinese fighter in international airspace. Also, U.S. ships are routinely dogged by Chinese aircraft and vessels during transits, particularly around manmade islands claimed by Beijing in the South China Sea.

Milley said there have been Chinese intercepts with Japan, Canada, Australia, Philippines and Vietnam. They all, he said, have seen a “statistically significant” increase in intercepts, and the number of unsafe incidents has increased by an “equal proportion.”

Milley, who met on Sunday with Gen. Andika Perkasa, chief of the Indonesian National Defence Forces, said Pacific nations like Indonesia want the U.S. military involved and engaged in the region.

“We want to work with them to develop interoperability and modernize our militaries collectively,” Milley said, in order to ensure they can “meet whatever challenge that China poses.”

He said Indonesia is strategically critical to the region, and has long been a key U.S. partner.

Milley, who spent the afternoon at Andika’s military headquarters, was greeted with a massive billboard bearing his photo and name, a military parade and a large television screen that showed a video of his career.

At the end of the visit, Andika told reporters that Indonesia has found China to be more assertive and “a little bit aggressive” with naval vessels in connection with terrirotiral disputes with his country.

Earlier this year, the U.S approved a $13.9 billion sale of advanced fighter jets to Indonesia. And in Jakarta last December, Blinken signed agreements for enhanced joint naval exercises between the U.S. and Indonesia.

China has condemned U.S. efforts to expand its outreach in the region, accusing America of trying to build an “Asian NATO.” During a speech in Singapore, Austin rejected that claim. “We do not seek a new Cold War, an Asian NATO or a region split into hostile blocs,” he said.