Japan scrambled warplanes after two Russian fighter jets briefly entered Japan’s air space near disputed islands on Thursday, Tokyo’s defence ministry said.

The planes were detected off the northern island of Hokkaido for just over a minute in what was reported to be the first breach of Japanese airspace by Russia. Four Japanese F-2 fighters were sent up to visually confirm the pair of Russian Su-27 fighters, according to Kyodo News.

“Today, around 3:00 pm (0600 GMT), military fighters belonging to Russian Federation breached our nation’s airspace above territorial waters off Hokkaido’s Rishiri island,” the foreign ministry said.

Japan’s foreign ministry lodged a formal protest over the incident, AFP reports.

However, Moscow denied any such intrusion had taken place, in a statement by the spokesman for the military command’s eastern district, Roman Martov.

“Flights by the air force of the Pacific Fleet take place regularly in the region, in strict adherence to the international rules, without violation of state borders,” it said.

The alleged incident came hours after hawkish Japanese premier Shinzo Abe said he wanted to find a “mutually acceptable solution” to the decades-old territorial row over the Russian-administered Southern Kurils, known as the Northern Territories in Japan, Reuters reports.