The U.S. defense secretary is urging Beijing to join in on regional cooperation or risk establishing a “Great Wall of self-isolation”, adding pressure on China from both the United States and Asian powers to rein in its actions in the South China Sea.

Ash Carter, U.S. Defense Secretary, encouraged China to contribute in a “principled security network” for Asia to help tackle concerns about its strategic intentions following “expansive and unprecedented actions” in the South China Sea.

Carter also s told the Shangri-La Dialogue, a regional security forum in Singapore, that the United States would remain the main guarantor of regional security for decades to come.

“I hope that this development doesn’t occur, because it will result in actions being taken by the both United States and … by others in the region which would have the effect of not only increasing tensions but isolating China” Carter said.

The South China Sea has become a crossroad between the United States and China, which is showing ever greater economic, political and military power in the region.

“The situation in the South China Sea continues to be viewed with concern,” Indian Defence Minister Manohar Parrikar told the forum. “All countries in the region need to recognize that our shared prosperities and the enviable rate of growth that this region enjoys over past decades will be put at risk by aggressive behavior or actions by any one of us.”

Japanese Defence Minister Gen Nakatani, speaking at the same event, said his country would help Southeast Asian nations build their security capabilities to deal with what he called unilateral and dangerous actions in the South China Sea.

“In the South China Sea, we have been witnessing large-scale and rapid land reclamation, building of outposts and utilization of them for military purposes,” Nakatani said, without mentioning China directly.

“No countries can be an outsider of this issue.”