Ganji was jailed in 2001 for writing articles in which he linked senior officials to the murder of dissidents. Correspondents say he is a hero to Iran's reformists for standing up to hardliners, and many world leaders have called for his release.

He has spent much of his jail term in solitary confinement and went on hunger strike for several months last year.

When brought to court to stand trial, Ganji complained he had been beaten and he says he was then threatened for revealing it.

Many Iranians thought Ganji, 46, would never be freed from jail, even though his sentence was due to end.

But Ganji's wife and lawyer confirmed he was sent home on Friday night, with no other pending charges against him.

The family says he is not in good health. He has low blood pressure and they say he now weighs only 49 kg, after having first been on a hunger strike and then later, they allege, denied regular food by the jail authorities.

But one family member told AFP news agency he was "doing well and in good spirits" after his release.

Ganji is not expected to give any interviews at this stage because his wife says that might give the authorities an excuse to arrest him again.

He came to prominence after his investigation of the murders in 1998 of five dissidents by intelligence agents.

The intelligence ministry said "rogue agents" had carried out the killings, but Ganji maintained that senior officials were behind them.

His release comes days before the United Nations security council is due to discuss Iran's stand-off with western nations over the country's nuclear programme.