(CNN) -- The Chinese government pledged to defend its territorial sovereignty Wednesday as reports surfaced that the Japanese government was in talks to purchase a disputed set of islands which both countries claim.
"Any unilateral actions taken by the Japanese regarding the Diaoyu Islands are illegal and invalid," said Hong Lei, a Chinese foreign ministry spokesman.
"China's will and determination to preserve its territorial integrity are resolute," Hong said. "We are closely monitoring the developments and will take necessary measures to defend our territorial sovereignty."
The uninhabited islands are known in Japan as Senkaku and in China as Diaoyu, and are owned privately by a Japanese family.
But both China and Japan claim the islands, which are located between Taiwan and Okinawa.
They sit among rich fishing waters and are also believed to be rich in oil resources.
Japanese media have reported that the central government and the city of Tokyo are in 2.05-billion-yen ($26.1-million) talks to buy the islands from the family that owns them
Japan's Chief Cabinet Secretary Osamu Fujimura would not confirm the details, but said negotiations with the owner were under way.
"We will announce once a result comes out," Fujimura said.
Animosity between China and Japan runs deep over the islands.
They 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 extends back hundreds of years. Japan says China ceded sovereignty when it lost the Sino-Japanese war in 1895.
Japan then sold the islands in 1932 to descendants of the original settlers.
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 Chinese analyst Guo Xiangang, 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," said Guo, the deputy director of the China Institute of International Studies, a think tank connected to China's Ministry of Foreign Affairs.
"There shouldn't be any discussion on Diaoyu Island. It has always been a part of China," he said.
In August, a diplomatic row erupted between Japan and China after a group of Chinese nationals were photographed raising flags there. They were arrested.
Japanese activists too have swum ashore, raising their flag, in incidents in 1990 and 1996.
In 2010, tensions rose to a boiling point when a Chinese fishing trawler rammed into a Japan Coast Guard vessel on patrol in the islands' waters.
Japan detained the crew members but later released them under Chinese diplomatic and trade pressure.
CNN's Chi Chi Zhang and Junko Ogura contributed to this report