WASHINGTON — China's behavior in a narrowly averted naval collision in the South China Sea was both "unhelpful" and "irresponsible," Defense Secretary Chuck Hagel said Thursday, warning against incidents that could escalate U.S.-Chinese tension.

"That action by the Chinese, cutting their ship 100 yards out in front of the [USS] Cowpens, was not a responsible action. It was unhelpful; it was irresponsible," Hagel told reporters at the Pentagon.

China on Wednesday acknowledged an encounter in early December between a Chinese naval vessel and the U.S. warship in the South China Sea.

China said its ship was conducting "normal patrols" when it encountered the U.S. missile cruiser, and its official news agency accused the United States of deliberate provocative behavior. But U.S. officials depicted the event differently.

They said the U.S. ship was forced to take evasive action to avoid collision.

Asked about Hagel's comments, Chinese Foreign Ministry spokeswoman Hua Chunying said: "For the U.S. and Chinese militaries to maintain a healthy and stable relationship that is beneficial to both countries, both sides must do their best to meet each other half-way."

The near collision came after Beijing's declaration of an air defense identification zone further north, in the East China Sea, ratcheted up tension and drew criticism from Washington, Tokyo and Seoul.

Experts have called the incident the most serious U.S.-Chinese maritime encounter in the disputed South China Sea since 2009.

Hagel said that such "incendiary" incidents had the potential to cause a "miscalculation."

"We need to work toward putting in place some kind of a mechanism in Asia-Pacific and with China . . . to be able to defuse some of these issues as the occur," he said.

General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, told reporters there had been no changes to rules of engagement given to forces in that region in order to prevent run-ins with China.

"What we do constantly though is we remain alert for changes in the environment," Dempsey said. "There are times that are more sensitive than others and we're in a heightened period of sensitivity. And you can count on our mariners and airmen to be aware of that."