Nuclear powers like China and the United States are free to sign a protocol to not violate the treaty but so far none of them have, largely because of differences over security assurances and the definitions of territory, much of which involves the disputed South China Sea.

In the past, Beijing has said it disagrees with the geographic delimitation of the zone but is willing to continue talks with Asean.

South China Sea: the dispute that could start a military conflict

On Wednesday, Fu Cong, director of the Chinese foreign ministry’s arms control department, said Beijing was prepared to endorse the protocol.

“Yes, China is ready to be the first to sign the Protocol to the Southeast Asian Nuclear-Weapon-Free-Zone Treaty,” Fu said in a tweet in response to a question by Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists in Washington.

Under the protocol, signatories would be obliged not to develop, manufacture or otherwise acquire, possess or have control over nuclear weapons in the treaty zone.

Testing or using nuclear weapons is also prohibited anywhere inside or outside the treaty zone that covers the continental shelf and exclusive economic zones – the boundaries of which are fiercely disputed by China and some Asean members.

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Washington’s hardened position on Beijing’s claims in South China Sea heightens US-China tensions

Washington’s hardened position on Beijing’s claims in South China Sea heightens US-China tensions

These challenges are raising the risk of regional conflict and concerns that countries in the region would have to take sides.

South China Sea: Beijing ‘ready to work with Asean’, defence chief says

Zhao Tong, a fellow with the nuclear policy programme at the Carnegie-Tsinghua Centre for Global Policy in Beijing, said that joining the treaty would be a symbolic move and do little to resolve China’s territorial disputes with its Southeast Asian neighbours.

“China seems to have deliberately embraced the ambiguities in many terms of the treaty, which would hardly change China’s nuclear policy and has nothing to do with how the country defines the boundaries,” Zhao said.

He said China could be trying to distance itself from the other major nuclear powers – which also include France, Russia and Britain – to present itself as a responsible partner in the region. There was an unspoken consensus among the five powers that they would have a united position on external issues like the treaty, and by saying it was prepared to sign the treaty, China could be trying to expose cracks in the consensus.

“If its rivalry with the US continues to escalate, China may have greater diplomatic incentive to embarrass the US and use the opportunity to just show that the US is dragging its feet internationally for its own benefit,” Zhao said.

“So far it seems China wants to reassure [others about] its positive position on the issue to win the support of the Southeast Asian nations.”

China’s first Type 075 ship to be based in Hainan amid South China Sea tension

Collin Koh, a research fellow at the maritime security programme at Nanyang Technological University in Singapore, said that while Beijing might want to be seen as a foremost partner to Asean and prompt Washington to sign up, the lack of trust between China and Asean members would be much harder to overcome.

“With or without acceding to the treaty, the underlying strategic trust deficit remains and this factor cannot be easily ameliorated simply with Beijing acceding to this treaty,” Koh said.

“At any rate, signing or not signing the treaty, Washington would not desire any impediment to its freedoms at sea, especially pertaining to military activities with whichever assets it deems necessary for its national interests in the region.”