Japan's Defense Ministry says Russian military aircraft breached Japanese airspace over the Pacific Ocean twice on Thursday.
It was the first intrusion by Russian military planes, or suspected to come from Russia, since 2015.
Ministry officials said two Tu-95 bombers entered Japanese airspace off Minami-Daitojima Island in the southern prefecture of Okinawa at around 8:53 a.m.
Japanese Air Self-Defense Force fighter jets scrambled and gave a radio warning to them. The bombers flew out of the airspace less than three minutes later.
The Russian planes continued to fly north. One of them breached Japanese airspace again at around 10:22 a.m., off Tokyo's Hachijojima Island.
The officials said the plane left the airspace about 2 minutes after the ASDF jets gave a radio warning.
The Japanese aircraft did not fire any warning shots against the intruders.
The officials said the bombers flew back toward Russia later.
Russia's defense ministry has rejected the claim, saying the flights were in full accordance with international law.
A Russian news agency quoted the ministry as saying the bombers flew over the neutral waters of the Sea of Japan, East China Sea, South China Sea and western parts of the Pacific Ocean as planned.