Another clash between Chinese fishing trawlers and Indonesian navy vessels in the South China Sea near Indonesia’s Natuna Islands on June 17 has led to sharp diplomatic exchanges. The confrontation followed a similar incident last month.

According to spokesman Edi Sucipto, the Indonesian navy intercepted 12 foreign vessels fishing illegally inside the 200-nautical-mile Exclusive Economic Zone (EEZ) around the Natunas. As Indonesian warships approached, the vessels fled. Warning shots were fired and eventually one Chinese flagged trawler was stopped and boarded. Its seven crew members were detained. No one was hurt.

Chinese Foreign Ministry spokeswoman Hua Chunying told a press conference on Sunday one of the fleeing boats was damaged by gunfire. One crew member was injured and hospitalised on Hainan Island, where he was recovering. Chinese coast guard vessels, she said, were immediately sent to the site “to protect Chinese fishing boats and fishermen and rescue and treat the injured.”

For the first time since last November, when Beijing formally recognised Indonesian sovereignty over the Natunas, China made clear that it maintained its territorial claims inside the EEZ around the island group.

Hua declared: “The incident took place in waters that are Chinese fishermen’s traditional grounds and where China and Indonesia have overlapping claims for maritime rights and interests.” She condemned the “wilful resort to force” and urged Indonesia to “stop taking actions that complicate, exaggerate the dispute and undermine peace and stability.”

On Thursday, Hua expressed hope that Indonesia could meet China “half way” in maintaining stability in the region.

However, Indonesian President Joko Widodo travelled to the area on Thursday, sending a blunt message to Beijing that his country would assert its sovereignty over the waters around the Natunas. Aboard a navy warship near the islands, which lie between Singapore and Borneo, Widodo held a meeting with members of his cabinet, discussing issues such as fishing, energy programs and military plans for the area.

The cabinet later issued a statement saying that the president’s visit was “an affirmation that the [Natuna] islands are the sovereign territory” of Indonesia.

Earlier, on Tuesday, Indonesian Maritime Affairs and Fisheries Minister Susi Pudjiastuti said China had previously said it had no sovereignty issues with Indonesia. At the same press conference, Rear Admiral A. Taufig R. accused China of trying to “mark out their territory” with the presence of coast guard vessels.

Behind these increased tensions is the tough stand on fishing and maritime rights taken by the Widodo administration, with the encouragement of the US. Washington has exploited every territorial dispute in the South China Sea to try to drive a wedge between China and its South East Asian neighbours. This tactic is part of the US “pivot to Asia” aimed at undermining Beijing’s influence and militarily encircling China in preparation for war.

Unlike the other nations in the region, particularly Vietnam and the Philippines, Indonesia does not have direct land claims against China. Jakarta has tried to maintain good relations with Beijing and act as a mediator in the region, even as Washington has pressed Jakarta for closer economic and military cooperation. Indonesia has strong trade and investment ties with China.

Evan Laksmana of the Jakarta-based Centre for Strategic and International Studies think tank told the Financial Times that if Beijing tried to enforce its position in the Natuna EEZ it would be harder for Jakarta to hold its neutral position on the South China Sea disputes.

In coming weeks, the United Nations Permanent Court of Arbitration in The Hague is expected to rule under the UN Convention on the Law of the Sea (UNCLOS) in a case brought by the Philippines, with Washington’s support and assistance, to challenge China’s maritime claims in the South China Sea.

If, as widely anticipated, the ruling favours the Philippines, the US is preparing for stepped-up diplomatic and military pressure on China, which does not recognise the jurisdiction of the court. Already, in a massive show of force, two US Navy carrier strike forces have been exercising this week in the nearby Philippine Sea.

Even after Widodo signed a US-Indonesian Strategic Partnership, Jakarta has proved reluctant to endorse the so-called “freedom of navigation” incursions by US warships within the 12-nautical-mile territorial limit around Chinese-controlled islets in the South China Sea.

Nevertheless, Indonesia has more aggressively defended its claims around the Natunas and is collaborating more closely with Washington. In October 2015, Jakarta signed a “Memorandum of Understanding on Maritime Cooperation” with the US and agreed to “work closely to combat and deter illegal, unreported, and unregulated fishing both in Indonesian waters and in the broader ASEAN region.”

This agreement includes US training in fisheries enforcement and access to vital US intelligence. The latter would include information from the extensive US satellite and maritime aircraft surveillance.

The Indonesian military, which has longstanding ties to US imperialism, has adopted a more aggressive attitude to China, in particular over the Natuna Islands. It has been pushing hard over the past few years to turn the small ramshackle garrison in the Natunas into what air force commander Agus Supriatna last year called “the Pearl Harbour of Indonesia.”

The government is funding plans for an upgraded airfield and port, along with moving marines, air force special units, an army battalion, three frigates, a new radar system, drones and five US supplied F-16 fighter aircraft to the island group. In the two incidents, this month and in May, naval frigates replaced fisheries vessels in confronting Chinese coast guard vessels.

Washington is increasing its involvement. On May 14, the US Senate Armed Services Committee voted for an amendment to the 2016 US Defence Authorisation Act, providing $425 million in funding over the next five years to boost “maritime security” in Asia—that is, the naval and coast guard capacities of China’s neighbours, including Indonesia.