Singapore's prime minister called on countries on Friday to break the "vicious cycle" of the South China Sea row, as the United States and China exchanged increasingly angry barbs over reclaimed islands in the disputed waterway.
Inaugurating Asia's biggest security forum, the Shangri-La Dialogue, Lee Hsien Loong also warned of the threat of Islamic State militancy in Southeast Asia and said it was not inconceivable that the ultra-radicals could establish a base in the region physically under their control, like in Syria or Iraq.
Just hours before Lee spoke, the Pentagon said China had placed mobile artillery weapons systems on a reclaimed island in the South China Sea.
U.S. Defense Secretary Ash Carter, who is to address the three-day Shangri-La Dialogue on Saturday, has called for a halt to the reclamation work, saying it was out of step with the regional consensus.
Admiral Sun Jianguo, a deputy chief of China's People's Liberation Army, will speak the following day.
Singapore's Lee said that if the rise of China in the international order was to remain peaceful, U.S.-Chinese relations had to remain strong.
"No country wants to choose sides between U.S. or China," he said.
But after weeks of angry rhetoric, the two sides were at loggerheads again on Friday.
The U.S. says China's actions undermine international law and interfere with the freedom of navigation in international waters. China says the islands are sovereign Chinese territory.
Pentagon spokesman Brent Colburn, who is travelling with Carter, said China's reclamation created "an air of uncertainty in a system that has been based on certainty and agreed-upon norms".
China's Xinhua news agency said some of the participants in the Shangri-La Dialogue "attempt to monopolies the right to speak in the field of international security."
"They echo each other, distort the truth, magnify differences, add fuel to fire, so that dialogue diverges from the path of strengthening exchanges and enhancing mutual trust."
Singapore's Lee said: "These maritime disputes...can and should be managed and contained. If the present dynamic continues, it must lead to more tensions and bad outcomes."
Islamic State base
Lee's comments on Islamic State were the strongest made by a regional leader on the threat posed by the radicals.
"The idea that ISIS can turn Southeast Asia into a wilayat - a province of a worldwide Islamic caliphate - is a grandiose, pie-in-the-sky idea," he said. "But it is not so far-fetched that ISIS could establish a base somewhere in the region, somewhere where the governments' writs do not run."
Hundreds of people from Southeast Asia have joined Islamic State forces in Iraq and Syria and regional security experts have warned of the dangers they may pose if they return.
Terrorism, maritime security and energy security are among the topics to be discussed at the three-day security dialogue, where defense ministers, military officers and international security experts from the United States, Europe and Asia are participating.
Aside from debate in open forums, most of the countries hold closed-door bilateral meetings, with over 200 such sessions scheduled according to the organizers.
Before events formally started on Friday, China's Admiral Sun held a series of bilaterals, including ones with Japan's Director-General of the Ministry of Defense, Hideshi Tokuchi and Vietnam's deputy defense minister General Nguyen Chi Vinh.
"We believe that through mutual cooperation the two parties will be able to solve the South China Sea dispute," Sun said on his meeting with Vietnam, which also has territorial claims in the region.
Malaysia, Taiwan, Brunei and the Philippines also claim parts of the sea.
John Chipman, director general of the International Institute for Strategic Studies that organizes the forum, said despite the sharp rhetoric from politicians, there has been improved dialogue between the militaries of the countries involved in the maritime disputes, which this weekend's meeting could build on.
"It will be interesting if the defense ministers point in their remarks to the importance of keeping that military dialogue going, whatever the political postures of the countries' leadership might be," he said.