Soldiers from the US, Indonesia and Australia joined a live-fire drill on Friday, part of annual joint combat exercises on Sumatra island amid growing Chinese maritime activity in the Indo-Pacific region.
A total of more than 5,000 personnel from the US, Indonesia, Australia, Japan and Singapore are participating in this year's Super Garuda Shield exercises, making them the largest since they began in 2009.
The expanded drills are seen by China as a threat. Chinese state media have accused the US of building an Indo-Pacific alliance similar to NATO to limit China's growing military and diplomatic influence in the region.
The United Kingdom, Canada, France, India, Malaysia, South Korea, New Zealand, Papua New Guinea and East Timor also sent observers to the exercises, which began early this month.
The US Indo-Pacific commander, Adm. John C. Aquilino, said the 14 nations involved in the training are signaling their stronger ties as China grows increasingly assertive in claiming virtually the entire South China Sea and holds exercises threatening self-ruled Taiwan.
"The destabilizing actions by the People's Republic of China as it applied to the threatening activities and actions against Taiwan is exactly what we are trying to avoid," he said at a joint news conference with Indonesian military chief Gen. Andika Perkasa in Baturaja, a coastal town in South Sumatra province.
"We'll continue to help deliver a free and open Indo-Pacific and be ready when we need to respond to any contingency," Aquilino said.
Indonesia and China enjoy generally positive ties, but Jakarta has expressed concern about what it sees as Chinese encroachment in its exclusive economic zone in the South China Sea.
Despite its official position as a non-claimant state in the contested South China Sea, Indonesia has been "dragged along" in the territorial dispute since 2010 after China claimed part of Indonesia's exclusive economic zone in the northern region of the Natuna Islands, said Connie Rahakundini Bakrie, a security analyst at the University of Indonesia.
The edge of the exclusive economic zone overlaps with Beijing's unilaterally declared "nine-dash line" demarking its claims in the South China Sea.
Increased activities by Chinese coast guard vessels and fishing boats in the area have unnerved Jakarta, prompting Indonesia's navy to conduct a large drill in July 2020 in waters around Natuna at the southern portion of the South China Sea.
Indonesia sees the current exercises with the US as a deterrent in defense of the Natuna Islands, while for Washington, the drills are part of efforts to forge a united front against China's military buildup in the South China Sea, Bakrie said.
"Indonesia wants to send the message that it is fully prepared for any high-intensity conflict in the South China Sea area," she said.
The joint combat exercises end Sunday.