Japan has warned China that violations of its airspace by surveillance balloons were “totally unacceptable”, as new information emerged that unidentified aerial objects that had entered Japanese airspace in recent years were likely Chinese spy balloon flights.

“As a result of further investigation of specific balloon-shaped flying objects that were confirmed in Japan’s airspace in the past, it is strongly suspected that they were unmanned surveillance balloons from China,” Chief Cabinet Secretary Hirokazu Matsuno told reporters on Wednesday.

Japan’s defence ministry said on Tuesday that it “strongly suspects” Chinese surveillance balloons had entered Japanese territory at least three times since 2019.

The ministry also said that it had “strongly demanded China’s government confirm the facts” of the incident and “that such a situation not occur again in the future”.

“Violations of airspace by foreign unmanned reconnaissance balloons and other means are totally unacceptable,” the ministry added.

According to international media reports, Beijing hit back on Wednesday, saying Japan lacked proof to support its accusations.

“Japan is making groundless accusations and smearing China without conclusive evidence. We are resolutely opposed to that,” China’s foreign ministry spokesperson Wang Wenbin told reporters.

Japan’s reassessment of past intrusions into its airspace has heightened since the United States shot down a Chinese balloon this month and briefed officials from 40 nations about the object, including Japan.

In the wake of the incident, the US military adjusted radar settings to detect smaller objects and discovered three more unidentified craft that US President Joe Biden also ordered shot down – one over Alaska, another over Canada and the third over Lake Huron of Michigan.