Japanese jet fighters fired warning flares at a Russian military reconnaissance plane that violated Japan’s airspace on Monday, Kyodo News and The Wall Street Journal reported.

A Russian IL-38 patrol plane entered Japanese airspace three times between 1pm and 4pm local time Monday as it flew over waters off Rebun Island, the northernmost part of Japan’s major Hokkaido island, Japan’s chief cabinet secretary, Yoshimasa Hayashi, said.

Tokyo has lodged an “extremely stern protest” with Moscow for the violation, Hayashi added.

According to him, Japanese Prime Minister Fumio Kishida instructed government officials to respond "firmly and calmly" to the airspace intrusion while closely collaborating with the United States and other nations.

On Monday, Japan’s air force scrambled F-15 and F-35 jet fighters in response to the first airspace violation, and the jets began firing flares during the third one-minute incursion by Russia around 3:42pm.

Japanese Defense Minister Minoru Kihara said the air force took the action only after issuing warnings to “the opponent.” He refused to comment when asked if the Russian patrol plane was flying with other Russian aircraft. The plane wasn’t undertaking particularly dangerous actions, he said.

The Russian plane violated Japan's airspace while Russian and Chinese navies were set out at the weekend to conduct naval exercises with warships in the Sea of Japan.

Russia’s Defense Ministry didn’t immediately respond to a request for comment on Japan's statement.