Japanese officials said Wednesday they are closely watching to see if China keeps its promise to prevent further violations of Japan’s airspace after explaining that an incursion by a Chinese military aircraft nearly three months ago was unintentional and caused by turbulence.

Tokyo protested and sought an explanation from Beijing after a Chinese Y-9 reconnaissance plane briefly entered Japanese airspace off the southern main island of Kyushu on Aug. 26, prompting Japan’s military to scramble fighter jets and warn the plane.

Chief Cabinet Secretary Yoshimasa Hayashi said China acknowledged the airspace violation and assured Japan that it would make efforts to prevent a recurrence.

“We take note of China’s explanation, and we will closely watch Chinese military activity from now on,” Hayashi said.

China said the airspace violation occurred when the plane’s pilot took emergency measures in response to turbulence in the area and was not intentional, Japan’s Foreign Ministry said. Japanese officials did not disclose further details, such as when China provided the explanation, citing the protocol of diplomatic exchanges.

Even though aircraft can encounter turbulence, such a significant deviation from a flight route is unthinkable, Japanese officials said.

NHK public television reported that Japanese defense officials said they still find the airspace violation unacceptable because it was a serious breach of territorial sovereignty.

In Bejing, Chinese Foreign Ministry spokesperson Lin Jian did not confirm what Japanese officials said they were told. He said only the diplomatic and defense ministries of the two countries have been communicating on the issue and that “China has no intention of intruding into the airspace of any country.”

Japanese officials are concerned about China’s growing military activity around Japan’s southwestern waters and airspace. It has led Tokyo to significantly reinforce its defenses in the area, which includes remote islands that are considered key to Japan’s defense strategy.

Japan is also worried about joint military activities between China and Russia.

A Chinese survey ship violated Japanese territorial waters off a southern island in August. In September, the Chinese aircraft carrier Liaoning and two destroyers sailed between Japan’s westernmost island of Yonaguni – just east of Taiwan – and nearby Iriomote, entering Japan’s “contiguous zone,” an area just outside of a country’s territorial waters in which it can still exercise some control over maritime traffic.

Also in September, Japan said its warplanes used flares to warn a Russian reconnaissance aircraft to leave northern Japanese airspace.

Russian and Chinese military activity has also ramped up near Alaska. In September, the U.S. military moved about 130 soldiers along with mobile rocket launchers to a desolate island in the Aleutian chain of western Alaska amid a recent increase in Russian military planes and vessels approaching American territory.

Eight Russian military planes and four navy vessels, including two submarines, came close to Alaska in September as Russia and China conducted joint military drills.

In July, two Russian Tu-95s and two Chinese H-6s entered the Alaska Air Defense Identification Zone, NORAD said. The bombers were intercepted by U.S. F-16 and F-35 fighter jets, along with Canadian CF-18s and other support aircraft, a U.S. defense official confirmed to CBS News.