Defending Malaysia’s new submission to the United Nations earlier this month, Saifuddin said: “It is a claim that we have made, and we will defend our claim. But of course, having said that, anyone can challenge and dispute, which is not something unusual.”

Saifuddin’s remarks came as Southeast Asian nations appear to be hardening their positions over the South China Sea, where long-running territorial disputes have been complicated by sabre-rattling and rivalry between Beijing and Washington.

China claims almost all of the South China Sea – through which US$5 trillion worth of goods are transported annually – and has built military outposts on artificial islands there despite overlapping claims by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

Zhang Mingliang, a Southeast Asian affairs expert with Jinan University in Guangzhou, said claimants may be using “precautionary” tactics to protect their interests.

“These moves are based on their own assessments and judgments,” Zhang said. “And they could also be part of efforts by local governments seeking to ease domestic political pressure.”

Meanwhile, despite a more conciliatory approach to Beijing under President Rodrigo Duterte, Manila last month announced an ambitious plan to expand its coastguard capacity. The government is seeking 4,000 new personnel for its coastguard teams by the end of this year and another 6,000 next year, according to Philippine newspaper the Inquirer.

The goal was to recruit an extra 25,000 personnel by 2025, the report said, as the country faced a growing challenge from Chinese coastguard and fishing vessels, which allegedly blocked Philippine boats during a stand-off over the Scarborough Shoal in 2012.

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Collin Koh, a research fellow at the S. Rajaratnam School of International Studies at Nanyang Technological University in Singapore, said the rival claimants may seek to consolidate their positions on the South China Sea “as much as possible” before a code of conduct is agreed.

China is negotiating with the 10-member Association of Southeast Asian Nations on the code of conduct – all rival claimants are Asean members – and the two sides aim to reach an agreement by 2021.

“Most of the parties may seek to exercise self-restraint in order to keep tensions under control, so as to facilitate an atmosphere conducive for the talks to proceed,” Koh said. “[But] some of the claimants may still continue with moves to consolidate their position in the South China Sea – in part to do so as much as possible before [the code of conduct negotiations] conclude and impose future restraint upon them, or to use such ongoing moves to strengthen their bargaining power in the talks.”

China’s claims over the South China Sea have increasingly been challenged by the United States and its allies, who regularly conduct so-called freedom of navigation operations through the waters. Beijing has accused the US and other nations of jeopardising stability in the region.

Koh said the US was likely to continue the patrols “as a way of impressing upon all parties involved in the [code of conduct] talks that such critical interests of international maritime user states – especially freedom of navigation and overflight – should not be in any way compromised in the negotiations”.

“FONOPs could be conducted to remind all parties in the talks, especially Asean governments, to bear in mind those external parties’ interests in the South China Sea,” he said.

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Malaysia’s submission to the UN came as a surprise to many observers, and other claimants have not opposed the move, suggesting the Asean members may be seeking to coordinate their efforts on the South China Sea.

“Asean parties will have a pretty challenging time to unite on a common set of positions versus China in the [code of conduct] talks,” Koh said. “[But] there’s still room for some form of coordination over specific issues that constitute common interests.”