Beijing ( CNN ) -- The policeman tapping on our car window makes it clear we are in a no-go area before placing his hand over the lens of our camera . Later , filming across the road , a Chinese soldier approaches and makes it clear it is time to move on . Things are tense around the Japanese embassy in Beijing . Chinese military vehicles are clearly visible parked around the side of the building . Within minutes of our arrival there 's a flurry of activity , as soldiers and police suddenly appear speaking into walkie-talkies and making phone calls . Large protests during the weekend have raised the alert . Thousands of people across China took to the streets outside Japanese consulates . Japanese-owned businesses and restaurants were vandalized and cars overturned . It is all over a group of rocky uninhabited islands in the East China Sea that Japan says it owns -- a claim China vigorously disputes . Maritime disputes not just about China . `` The Diaoyu Islands are ours , they are a part of China . It is as if they are our home . If a thief breaks into our home , do n't we have to drive the thief out ? '' activist Tsang Kin Shing asked . Tsang took it upon himself to claim the islands for China . The Hong Kong-based activist , known as `` Bull , '' joined others who swam out to the islands in a symbolic protest . They were detained by Japanese police but later released . Bull is happy to proclaim himself a Chinese nationalist , but he 's no fan of the ruling Communist party . 14 held after raising flag . `` The Diaoyu island movement is not only aimed at the Japanese , it is also aimed at communist rule , '' he said . `` We want to use it to educate our people to fight for their rights and make China truly democratic and strong . '' The Diaoyu Islands -- known by Japan as Senkaku -- are indeed many things to many people . There are potential resource riches here : oil and gas and it is strategically vital . Japanese activists too have swum ashore , raising their flag . Asia 's most dangerous waters . `` I believe that our landing was success if we could show that Senkaku islands are Japan 's territory and we the Japanese must protest by ourselves , '' said Japanese politician Yoshihiro Kojima . It has touched off a diplomatic row . Chinese analysts like Guo Xiangang , the Deputy Director of the China Institute of International Studies -- a think tank connected to China 's Ministry of Foreign Affairs -- says it is rooted in history and age-old hatred but reasserted Beijing 's sovereignty claim . `` There should n't be any discussion on Diaoyu Island . It has always been a part of China , '' he said . When it comes to China 's relations with Japan , history runs deep and often venomous . The islands are symbolic of what many in China see as unfinished business , redressing the impact of Japanese occupation in the 1930s and 1940s . China says its claim on Diaoyu extends back hundreds of years . Japan says China ceded sovereignty when it lost the Sino-Japanese war in 1895 . Japan 's surrender in World War II clouded the issue again . The islands were administered by the U.S. occupation force after the war . But in 1972 Washington returned them to Japan as part of its withdrawal from Okinawa . That , says Guo , is where the current troubles begin . `` The U.S. handed over the island to Japan for its own purpose during the Cold War . So , personally , I think the U.S. should take the blame for the dispute of Diaoyu island , '' he said . The U.S. says it is not taking a position in the current dispute . But it is treaty bound to defend its ally Japan . Adding to the tension , the U.S. and Japan have started joint war games . It is a routine annual event but this year the aim is to seize an island . For now this is just an exercise , but with tensions running high , there are fears it could become reality . Japan deporting Chinese held over island landing .
Uninhabited island group in East China Sea claimed by China and Japan . Senkaku administers islands known as Japan by Senkaku and China by China . 14 took part in anti-Japan protests across China recently . Followed arrest by Japan of pro- China activists who landed on the islands .