US Defense Secretary Ash Carter told the Shangri-La Dialogue in Singapore that China was threatening security in the region with its maritime construction work, but acknowledged other claimant countries to the disputed sea were also at fault.

“There’s no progress in the South China Sea (dispute), but the atmosphere has calmed a bit, thanks to reasonable consideration by all parties,” said Major General Jin Yinan of China’s National Defense University, a delegate at the conference. “The US has adjusted its stance a little.”

Admiral Sun Jianguo, a deputy chief of staff of the People’s Liberation Army who headed the Chinese delegation, refrained from singling out the United States for criticism in his address and emphasized China’s commitment to peaceful relations.

“China has always kept in mind the larger interests of maritime security,” Sun said, reiterating that his country’s “indisputable” claims over the waters were based on legal and historical evidence.

Nevertheless, Washington is under huge pressure to respond forcefully to the Chinese land reclamation, with Republican Senator John McCain, one of the participants at the dialogue, suggesting that US ships and aircraft ignore the 12-nautical mile zone around the artificial islands.

“If we respected a 12-mile zone, then we would be making a mistake of enormous proportions because that would be de facto recognition of Chinese sovereignty,” said McCain, the chairman of the Senate Armed Services Committee.

If US vessels enter the zone, tensions would escalate sharply and there is no saying how Chinese forces based there would respond.

“If you look at the rhetoric, they are going to fight back,” said Jia Qingguo, Dean of the School of International Studies at Peking University. “If you look at their interests, they may opt for rhetoric instead of action. But here the danger is of an accident-led conflict.”

Admiral Harry Harris, newly appointed chief of the US Pacific Command, told reporters his forces would continue to operate in the region “without limitation and in accordance with international law.”

But he also said he wanted increased military-to-military ties with China, including the US-led Rim of the Pacific (RIMPAC) joint naval exercises in 2016.

McCain and other critics of the administration have said China should be barred from RIMPAC to show US disapproval of its actions.

China also signalled it was not considering declaring an Air Defense Identification Zone (ADIZ), which requires overflying aircraft to identify themselves, around the disputed islands anytime soon.