Several Japanese self-defense force fighter jets were scrambled early Wednesday after Russian military aircraft were spotted near Japan's airspace. The Russian aircraft remained in the area for 12 hours. Japan's Defense Ministry says, two Russian TU-95 bombers and an A-50 surveillance jet approached Western Japan over the Sun in region on Wednesday morning. Japanese fighters immediately took off and tracked them. The Ministry says the two bombers stayed near the Japanese archipelago for 12 hours, while the A-50 circled over waters of Sun in for 9 hours. The A-50 is equipped with an early airborne warning and control system. Around midday, another two S-U-24 surveillance planes approached Japanese airspace between Hokuriku and Hokkaido in northern Japan. They stayed over the Sea of Japan for several hours. None of the planes intruded into Japanese airspace, but the Ministry says it's unusual for Russian military aircraft to fly in such numbers so close to the country. The Ministry says it's the first time Russian planes equipped with early warning systems have been spotted near Japan. It says the Russian Air Force may have been conducting sophisticated surveillance drills. The Japanese think tanks says China is strengthening its military capabilities to protect and expand its maritime interests. It asserts that China is obliged to explain the reasons for intensifying its marine activities to neighboring nations and the international community. The National Institute for Defense Studies released on Friday a report on China's recent rapid military buildup. The report says China wants to pursue economic development and military strategy through maritime tactics. It maintains that the country is deploying ships and aircraft with good maneuverability to strengthen patrols in the South and East China Sea. The report notes that China is becoming increasingly cautious of a new U.S. defense strategy that places importance on the Asia-Pacific region. The brief ads China wants to boost deterrence by demonstrating its military operational capabilities. It includes that Chinese policy could move in one or two directions. The country could pursue a hard line, unyielding stance, or use its growing power for stability with international partners. Japan's Coast Guard is on high alert against increased activity by Chinese maritime survey vessels in Japan's exclusive economic zone in the East China Sea. The two countries are supposed to give prior notice before carrying out surveys in the other side's zone, but the Chinese side is ignoring the agreement and continuing its activities. The Coast Guard used to spot the ships only a few times a year, but recently there have been seen every month. Seven cases have been reported since July. The Coast Guard says it receives notification from China, but many of the vessels are in areas other than those specified. It says the Chinese ships insist they are conducting legitimate research when they reply to warnings from surveillance vessels or planes, but some ships do not respond to the calls. The Coast Guard adds that more Chinese fisheries surveillance vessels are being spotted near the Senkaku Islands in Okinawa prefecture, following the collision incidents in September last year. China wants to investigate the seabed and natural resources in the East China Sea partly for military purposes. By entering the zone many times, they are aiming to protect their interests in the East China Sea. The boats have appeared 14 times so far, and one of them intruded into Japanese maritime territory in August for the first time. These defense officials say to Russian bombers took an unusual course circling around Japan. The Defense Ministry says to T.U. 95 bombers from the Russian Air Force approached Japanese airspace near the Strait of Tsushima on Thursday morning. Fighter planes from Japan's Air Self Defense Force scrambled to track the bombers. The aircraft later flew southward over the East China Sea, and then south of Okinawa's main island. Afterwards, it moved to the Pacific side before skirting along the Japanese archipelago northward. The bombers continued flying over the Strait of Tsoya while being fueled midair. They then headed south on the Japan Sea side before leaving areas near Japan. The Defense Ministry says the bombers did not violate Japan's airspace, but it was an unusual route for any Russian military aircraft. The Russian Air Force has been active around Japan recently. Bombers and spy planes have approached Japanese airspace five times since last month.