SINGAPORE-  U.S. Defense Secretary Ash Carter today said that Beijing's island-building in the South China Sea was undermining security in the Asia-Pacific but, despite his blunt remarks, the response from Chinese officials was measured.

Carter, speaking to top defense officials from the Asia-Pacific at the annual Shangri-La Dialogue in Singapore, acknowledged that several countries had created outposts in the region's disputed islands, but he said the scope of China's activity created uncertainty about its future plans.

"China has reclaimed over 2,000 acres, more than all other claimants combined ... and China did so in only the last 18 months," Carter told the Shangri-La Dialogue security forum. "It is unclear how much farther China will go."

He said the United States was "deeply concerned" about the scale of China's land reclamation and the prospect of further militarization of the islands, saying it would boost "the risk of miscalculation or conflict."

However, he added: "We all know there is no military solution to the South China Sea disputes. Right now is the time for renewed diplomacy, focused on a finding a lasting solution that protects the rights and interests of all."

A Chinese military delegate to the forum said Carter was wrong to criticize China, but his comments were not as hostile as those made at the Shangri-La Dialogue in past years.

"This year, Carter's speech is more balanced...It's helpful for building new ties between China and the U.S. as major powers, and also helpful to improving military relationships," Senior Colonel Zhao Xiaozhuo of China's Academy of Military Science told reporters on the sidelines of the forum.

Bonnie Glaser, of the Center for International Strategic Studies, said both China and the United States were trying to tone down the rhetoric after angry exchanges at the event last year.

"Carter's trying not to be too harshly targeting of China but at the end of the day the real problem is China and everyone knows that," she said.

The official Chinese response will only come on Sunday when Admiral Sun Jianguo, the head of Beijing's delegation, addresses the conference.