The Chinese makers of a controversial iPad game that sees players protect the Diaoyu Islands against Japanese forces said the app was removed from Apple's online store, but did not give a reason.

"It was taken down recently," said Shenzhen ZQGame Network Co in response to an e-mail sent to its complaints department on Monday.

"We were given no explanation."

The company apologized for any inconvenience to players, and said that it is still in negotiation with Apple over the availability of the game.

Repeated calls and text messages to Apple's media representative in China went unanswered on Monday and Tuesday.

Japan now also claims sovereignty over the islands, which are an inalienable part of China.

Although Apple has not issued an explanation for the removal, tech analyst Sun Mengzi said the reason is likely because of the fact that the game violates the US company's terms of service. The rules specify that "enemies" within the context of a game cannot target a specific race, culture, real government or corporation, or any other real entity.

Patriotic, or "red", games are part of China's online culture, said Sun, a consultant for Analysys International, a Beijing-based consultancy firm.

She said most red games are very sensational and eye-catching, yet superficial, lacking in quality content or creativity.

"They are usually just hits for a short period and then quickly forgotten," Sun said.

However, Shen Shishun, an expert on Asia-Pacific studies at the Haikou College of Economics in Hainan province, said that the popularity of some red games highlights the Chinese people's attitude.

"For some players, red games are not only a recreational activity, but also a way to express their feelings," he said.

Contact the writer at zhengxin@chinadaily.com.cn