China’s declaration last year of an air-defense identification zone over disputed islands in the East China Sea has increased tensions with Japan, the top U.S. Air Force commander in the Pacific said Thursday.

There have been unsafe midair encounters, like a Chinese jet that came within 30 feet of a U.S. Navy P-8 Poseidon plane in August, Gen. Herbert "Hawk" Carlisle told reporters.

But interactions between Chinese, Japanese and U.S. aircraft in the area have been very safe to a large extent, he said.

"The good news is that both nations, and the U.S. included, have been very good about staying separate and not getting into a case where we are too close or we risk miscalculation," Carlisle told a group of reporters at the headquarters of Pacific Air Forces in Hawaii.

The U.S. is talking to China about the unsafe intercepts, he said. The unsafe encounters have generally been isolated to one place and limited to one Chinese unit, he said.

Carlisle said he believes Chinese leaders know this situation and they are addressing the matter. "They have made statements that they want to be safe, they know the cost of miscalculation and the tragedy that could happen," he said.

China declared the zone last November, saying all aircraft entering the area must notify Chinese authorities and are subject to emergency military measures if they do not identify themselves or obey orders from Beijing. It said it would "identify, monitor, control and react" to any air threats or unidentified flying objects coming from the sea.

The zone includes a chain of islands — known as the Senkaku in Japan and the Diaoyu in China — that are controlled by Tokyo but also claimed by Beijing.

Carlisle said the zone has put Chinese planes and Japanese planes in close proximity more frequently as each flies inside what they consider to be their own air defense-identification zones.

Japan is a U.S. ally, and the U.S. has vowed to defend Japan in a potential clash over the islands.

Carlisle will soon be moving to Virginia to lead the Air Combat Command. He will hand over command of Pacific Air Forces to Lt. Gen. Lori Robinson during a ceremony next week.