Thursday about a graft probe in Namibia involving a firm linked to the son of President Hu Jintao, as the state-run media ignored the sensitive issue.

Two Namibians and a Chinese national were arrested last week in Namibia as part of a probe into bribery allegations involving Nuctech, a company headed until last year by Hu's 38-year-old son, Hu Haifeng.

Searches for information on the case and Hu Haifeng's connection to it on Chinese Web portals turned up error messages such as: "The search results may contain content not in line with relevant laws, regulations and policies."

Such results on China's heavily-censored Internet are typically returned when a Web user seeks banned information.

China has a history of blocking access to sensitive data on the Internet, especially concerning politics and the lives of top leaders.

Popular sites such as Facebook, YouTube and Twitter have been blocked for weeks as censors sought to limit the information flow over deadly unrest in Xinjiang and the 20th anniversary of the Tiananmen massacre.

The US-based China Digital Times, which monitors Web developments in China, said propaganda officials had issued an order banning various Internet searches related to the Nuctech case.

China Digital Times and media watchdog Reporters Without Borders said it appeared the Nuctech Internet censorship had been in place for a few days.

China's mainstream media is more tightly controlled by the government, and newspapers as well as television news have also made no mention of the Nuctech case in recent days.

Hu Haifeng was president of Nuctech, which provides scanning technology, until last year, when he was promoted to Communist Party secretary of Tsinghua Holdings, which controls Nuctech and more than 20 other companies.

The three arrested in Namibia are accused of graft over a series of bank transfers allegedly linked to a 55.3-million-dollar contract Nuctech had won to supply the nation with security scanning equipment, court officials there told AFP earlier.

Staff at Nuctech's Beijing-based headquarters declined to comment on the case when contacted by AFP.

"'We never speak to the media," said a woman who answered the phone.