SHANGHAI, CHINA: Hackers calling themselves the Iranian Cyber Army briefly hijacked the home page of China's top search engine, Baidu Inc, on Tuesday weeks after doing the same thing to Twitter.com.

Media carried screenshots of Baidu's home page showing a message: "This site has been hacked by Iranian Cyber Army" against a dark background and the flag of Iran.

The group hacked popular microblogging website Twitter in December replacing Twitter's home page with the same headline and an anti-American message.

While Twitter played an important role in enabling communication during last June's Iranian students protests, it is not clear why Baidu's website (www.baidu.com) was targeted. Experts told Reuters last month that the Iranian government was not likely to be involved.

China and Iran enjoy a relatively good relationship based on energy and Chinese state companies sell gasoline to Iran.

"This morning, Baidu's domain name registration in the United States was tampered with, leading to inaccessibility," said Baidu in a statement emailed to Reuters.

Baidu's search engine was down for at least four hours.

Baidu leads U.S. search giant Google Inc in China's search market with more than 60 per cent of market share.