Attorney General Sharif Shadi announced the move after a 45-minute hearing. He gave no details.

The men are reported to belong to the strict Salafi movement - a branch of the Wahhabi sect.

Some of them had previously been held - and released - for allegedly being linked to al-Qaeda, their lawyer said.

No weapons

"They can all go home. They are no charges against them," said Mr Shadi, announcing the move.

Defence lawyer Abdulla Hashim said: "No weapons and no dangerous materials were found either in their own homes or those of their friends or relatives."

Bassam al-Ali, Bassam Bukhowa, Yasser and Omar Kamal and Mohedin and Ali Khan were arrested in a pre-dawn raid on Tuesday.

Bahrain is a liberal island in the Gulf

Interior Minister Sheikh Rashed al-Khalifa told the Bahrain News Agency that the arrests were made after security forces searched several areas.

"[They] arrested six people to prevent them from committing dangerous operations that would have threatened people and their possessions," he said.

Bahrain hosts the United States Fifth Fleet and is home to a large number of expatriates living among an indigenous population of about 400,000 people.

Mr Ali was arrested in February 2003 for allegedly running a terror cell but was released in June for lack of evidence.

Sheikh Mohammad Saleh - who was not seized even though his home was searched on Tuesday - was arrested in Saudi Arabia last July and released in April.

Liberal society

The suspects are variously reported to be followers of the extremist Sunni Salafi movement, which is close to Bin Laden's al-Qaeda, or Wahhabis - the prevailing sect in neighbouring Saudi Arabia.

The island state of Bahrain is a far more open and liberal society than Saudi Arabia, which can be reached by just a short drive over the King Fahd causeway.

Alcohol is sold openly and bars, nightclubs and cinemas are permitted.