JAKARTA, Indonesia — U.S. and Indonesian militaries began annual joint combat drills on the Indonesian island of Sumatra on Wednesday, joined for the first time by participants from other partner nations, signaling stronger ties amid growing China’s growing maritime activity in the Indo-Pacific region.

More than 5,000 troops from the United States, Indonesia, Australia, Japan and Singapore participated in this year’s exercises, making them the largest since the exercises were established in 2009. The exercises are designed to build interoperability, capacity, trust and cooperation in support of a free and open Indo-Pacific, the U.S. Embassy in Jakarta said in a statement.

“It is a symbol of the U.S.-Indonesian bond and the growing relationship between ground forces in this important region,” Gen. Charles Flynn, commanding general, U.S. Army Pacific, said in the statement. “Because land forces are the glue that holds the region’s security architecture together.”

Flynn and Indonesian military leader General Andika Perkasa opened the joint drills with a ceremony Wednesday morning in Baturaja, a coastal city in South Sumatra province. The drills will last until Aug. 14, encompassing Army, Navy, Air Force and Navy drills.

The planned two-week drills began after China’s Defense Ministry said Tuesday night that it would carry out a series of targeted military operations to “safeguard national sovereignty” in response to the House Speaker’s visit. United States, Nancy Pelosi, in self-governing Taiwan, which China claims as part of its territory to be annexed by force if necessary.

China has also been increasingly assertive over its claim to nearly all of the South China Sea.

US General Mark Milley, chairman of the Joint Chiefs of Staff, said the number of interceptions by Chinese aircraft and ships in the Pacific region with US forces and other partners has increased significantly over the past of the last five years, and the number of dangerous interactions has increased in similar proportions.

“The message is that the Chinese military, in the air and at sea, has become much more and significantly more aggressive in this particular region,” Milley said last month during an Indo-Pacific trip that included a stopover in Indonesia.

Milley said Indonesia was strategically critical to the region and had long been a key partner of the United States. Earlier this year, the United States approved a $13.9 billion sale of advanced fighter jets to Indonesia. And in Jakarta last December, Secretary of State Antony Blinken signed agreements for enhanced joint naval exercises between the United States and Indonesia.

While Indonesia and China enjoy generally positive relations, Jakarta has expressed concern over Chinese encroachment on its exclusive economic zone in the South China Sea, which China claims virtually in its entirety.

The U.S.-Indonesian military drills coincided with Pelosi’s arrival in Taiwan on Tuesday night as the highest-ranking U.S. official in 25 years to visit the self-governing island. Beijing views visits by foreign government officials as an acknowledgment of the island’s sovereignty.

Japan’s Ground Self-Defense Force is taking part in the exercises for the first time, saying it promotes a “free and open” Indo-Pacific view of security and trade with the United States and other democracies in the region.

The expanded exercises are seen by China as a threat. Chinese state media have accused the United States of building an Indo-Pacific alliance, similar to NATO, as a means of intentionally provoking conflict.