AP TOKYO JAPAN’S purchase of several disputed islands from their private owners was aimed at keeping nationalist activists at bay and reducing tensions with China, but now the government must deal with Beijing’s anger over the move.

Prime Minister Yoshihiko Noda’s administration was left with little choice but to buy the rocky outcroppings in the East China Sea after the stridently nationalistic governor of Tokyo, Shintaro Ishihara, announced a plan in April to buy the islands from their Japanese owners and then develop them to ensure that they would never be sold to China. The prospect of construction on the islands and boatloads of activists landing on their shores would be sure to upset China, so the central government stepped in Tuesday to buy the islands for $26 million. It has no plans to develop them.

Beijing’s response was swift and strong, calling the purchase “null and void” and threatening “serious consequences.” China sent two patrol ships to waters near the islands, according to the official Xinhua News Agency, although Japanese coast guard officials said no Chinese ships had been sighted within 38 kilometers of the islands as of Wednesday afternoon.

“There’s no doubt that the purchase was caused by Ishihara’s initiative,” said Koichi Nakano, a political science professor at Sophia University in Tokyo. “It’s a severe loss of face for the Chinese.They’ll feel the need to do something” in response.

In Beijing, Luo Zhaohui, director-general of Asian affairs at China’s Foreign Ministry, told a Japanese diplomat on Wednesday that China will not tolerate any unilateral act by Japan and asked Japan to immediately revoke its purchase of the islands, known as Senkaku in Japan and Diaoyu in China.

Analysts said that while prospects for military conflict remained remote, tensions between the two Asian giants would likely remain high for some time. In a move meant to assert its sovereignty, China announced coordinates marking areas off the Islands that it considers its territory.

China might also cancel some Japan-related events. In 2010, it stopped exports to Japan of rare earth metals that are used in high-tech manufacturing after Tokyo arrested a fishing boat captain whose trawler collided with two Japanese patrol boats off the disputed islands. Still, China doesn’t want too much trouble while it undergoes a major leadership transition this fall, and both nations presumably don’t want to damage their vital economic relationship.