A territorial flare-up between China and Japan intensified Tuesday as two Beijing-sent patrol ships arrived near disputed East China Sea islands in a show of anger over Tokyo's purchase of the largely barren outcroppings from their private owners.

The China Marine Surveillance has drawn up a plan to safeguard China's sovereignty of the islands and the ships were sent to assert those claims, said the Chinese government's official news agency, Xinhua. The marine agency is a paramilitary force whose ships are often lightly armed.

The rocky islands, known as Senkaku to Japanese and Diaoyu to Chinese, have been the focus of recurring spats between the countries and also are claimed by Taiwan. The China-Japan dispute has been heating up in recent months, in part because the nationalist governor of Tokyo proposed buying the islands and developing them.

Japan's central government announced its own deal this week with the Japanese family it recognizes as the owner. Chief Cabinet Secretary Osamu Fujimura told reporters the government budgeted 2.05 billion yen ($26 million) for the purchase "to maintain the Senkakus peacefully and stably."

Public broadcaster NHK said the government and the family signed a deal Tuesday.

The central government does not plan to develop the islands. Several experts interpreted the move as an attempt to block the plan by Tokyo Gov. Shintaro Ishihara, which could have raised tensions further. Ishihara also had said he hoped to visit the islands in October.