A Russian military patrol plane breached Japanese airspace off the country’s northwestern coast three times on Monday, prompting Japan’s military to dispatch a fighter jet to issue radio warnings and, for the first time, to use a signal flare to deter the Russian aircraft.

       According to Yoshimasa Hayashi, the chief cabinet secretary to Prime Minister Fumio Kishida, the Russian plane flew above Rebun Island, which is northwest of Hokkaido, Japan’s northernmost prefecture, between 1 p.m. and 3 p.m. on Monday.

       “This violation of our airspace is extremely regrettable,” said Mr. Hayashi, in remarks to reporters on Monday afternoon. “We have lodged an extremely strong protest with the Russian government through diplomatic channels and have strongly urged them to prevent a recurrence.”

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