JAKARTA, Indonesia (AP) — The Association of Southeast Asian Nations began its first joint naval exercise on Tuesday at a time when several member countries are responding more strongly to increasing Chinese assertiveness in the area.

The non-combat drills, named ASEAN Solidarity Exercise, include joint maritime patrol operations, search and rescue operations, and humanitarian and disaster relief, Indonesian military chief Adm. Yudo Margono said.

He said the five-day exercise in Indonesia’s Natuna waters aims to boost military ties among the ASEAN nations and enhance interoperability. The drills also involve civilian groups involved in humanitarian relief and disaster prevention.

ASEAN nations have taken part in naval exercises before with other countries — including both the United States and China — but this week’s drills are the first involving just the bloc and are being read by many as a signal to China.

China’s “nine-dash line,” which it uses to demarcate its claim to most of the South China Sea, has brought it into tense standoffs with rival claimants Vietnam, Malaysia, Brunei and the Philippines, with Chinese fishing boats and military vessels becoming more aggressive in the disputed waters.

The line also overlaps with a section of Indonesia’s exclusive economic zone extending from the Natuna Islands. Margono initially said the exercises would take place in the North Natuna Sea at the edge of the South China Sea, a fault line in the rivalry between the U.S. and China, following meetings of ASEAN defense officials in Bali in June.

However, Indonesia, which holds the rotating chair of ASEAN this year, decided to move the drills to the South Natuna Islands, away from the disputed area, apparently to avoid any reaction from Beijing.

China and ASEAN signed a nonbinding 2002 accord that called on rival claimant nations to avoid aggressive actions that could spark armed conflicts, including the occupation of barren islets and reefs, but violations have persisted.

China has come under intense criticism for its militarization of the strategic South China Sea but says it has the right to build on its territories and defend them at all costs.

“Those who carry out any exploration or activities in that area must not violate state territory,” Margono said after an opening ceremony for the exercise attended by ASEAN military leaders on Batam island next to Singapore. “That has been clearly regulated by the United Nations Convention on the Law of the Sea.”

Asked whether ASEAN was sending a stronger message against China’s competing territorial claims in the South China Sea, Margono replied, “We have had a firm stance.”

He told reporters that ASEAN has agreed to hold military exercises annually. In the future, they will be expanded to full war drills involving the army, navy and air force, he 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. Increased activities by Chinese coast guard vessels and fishing boats in the area have unnerved Jakarta, prompting its navy to conduct a large drill in July 2020 in waters around Natuna.

Despite its official position as a non-claimant state in the South China Sea, Indonesia renamed part of it the North Natuna Sea in 2017 to underscore its claim that the area, which includes natural gas fields, is part of its exclusive economic zone. Similarly, the Philippines has named part of what it considers its territorial waters the West Philippine Sea.

Vietnam, one of the four ASEAN claimant states, has been vocal in expressing concerns over China’s transformation of seven disputed reefs into man-made islands, including three with runways, which now resemble small cities armed with weapons systems.

Two ASEAN members, Cambodia and Laos, both Chinese allies, have opposed the use of strong language against Beijing in the disputes.