Japan's Defense Minister Itsunori Onodera Sunday expressed concerns over Russian bombers'recent frequent spot near its territory, according to local media.

Russia's move was "abnormal" and even "not seen in the Cold War era," and Japan "will continue to monitor closely" the Russian aircraft, Onodera was quoted by Kyodo News as saying at an Air Self-Defense Force (ASDF) base in Naha, Okinawa Prefecture.

The ASDF scrambled fighter jets for seven days in a row through Saturday after it detected a number of Russian military aircraft flying around the Japanese archipelago, said Kyodo.

The Japanese Defense Ministry is analyzing the motives behind the Russia's move, but Onodera said he has not received any report from SDF personnel stationed in Russia, said the report.