TOKYO (AP) -- Chinese and Japanese government ships exchanged warnings Friday in waters near disputed islands in the East China Sea, while Tokyo called on Beijing to protect its citizens amid anti-Japan protests and reported assaults in China.

Tensions between the Asian giants have flared anew after the Japanese government bought the islands from their private Japanese owners this week. The uninhabited islands, claimed by both countries as well as Taiwan and called Senkaku by Japan and Diaoyu by China, have become a rallying point for nationalists on both sides.

In response to Japan’s purchase, China on Friday sent six surveillance ships into what Japan says are its territorial waters around the islands. After Japanese coast guard ships radioed warnings to the Chinese vessels, two or three moved beyond the territorial waters but the others remained within the 12-mile zone around the islets, said Yasuhiko Oku, a Japanese coast guard official.

While Japan controls the islands, which are surrounded by rich fishing grounds and are near key shipping lanes, China doesn’t recognize those claims and its ships issued their own warnings to the Japanese coast guard vessels. State-controlled China Central Television repeatedly played footage of a Chinese Marine Surveillance officer aboard one of the ships radioing the Japanese vessels to demand they leave.

“The actions of your ships violate China‘s sovereignty and rights,” the officer was shown saying. “Any unilateral act from your side regarding the Diaoyu islands and its affiliated islands is illegal and invalid. Please stop any infringing acts. Otherwise, your side will bear the consequences caused by your actions.”

Emotions have been running high since April, when Tokyo’s nationalistic governor, Shintaro Ishihara, proposed buying and developing the islands so that they wouldn‘t fall into Chinese hands. Activists from both sides landed on the islands in August.

To block Ishihara’s plan, which would have infuriated China, Prime Minister Yoshihiko Noda‘s government was left with little choice but to buy the islands. The government doesn’t plan to develop them, but the move has still angered China, and Beijing has warned of “serious consequences.”

Anti-Japanese protests have since been held in various Chinese cities, and state media has published calls for a boycott of Japanese goods.

The Japanese Consulate in Shanghai reported on its website that there have been several Japanese have been assaulted or harassed in the past few weeks. It said Chinese have thrown water bottles and hurled insults at Japanese walking on the street. One person was hit with soda by a Chinese person who shouted “Japanese!” It did not give a specific number of assaults.

The consulate warned Japanese in China to take precautions and avoid crowds and demonstrations and being out late at night.

Japanese Chief Cabinet Secretary Osamu Fujimura called on Beijing to take steps to assure the safety of Japanese tourists and residents in China.

Officials both in Tokyo and Beijing maintained that they had the right to send ships to the islands.

China‘s foreign ministry said its decision to send its ships was part of legal “law enforcement and patrol activities aimed to demonstrate China’s jurisdiction over the Diaoyu Islands.” Fujimura called the fleet‘s deployment an unprecedented violation of Japanese territory.

“It is extremely regrettable,” he said, adding that Japan was “taking all possible measures to be ready for any development.”

Japan summoned China’s ambassador to lodge a protest.

On Thursday, two Taiwanese coast guard patrol ships sailed to 25 nautical miles west of the disputed islands. The Taiwanese coast guard said the vessels demonstrated the coast guard’s ability to protect local fishermen.