Mordechai Vanunu, the technician who revealed that Israel had nuclear weapons, has begun a three-month jail term for violating the terms of his release in 2004.
Mr Vanunu was convicted by an Israeli court in December 2009 and sentenced to six months' community service.
He refused, saying he would be in danger of being assaulted by a member of the Israeli public.
The court then returned him to jail instead.
Mr Vanunu spent 18 years in jail for revealing the existence of the clandestine Israeli nuclear programme.
Before being led away he shouted "You didn't get anything from me in 18 years; you won't get anything in 3 months. Shame on you, Israel."
He was arrested on suspicion that he met foreigners, violating conditions of his 2004 release from jail.
His lawyer said his arrest was because of his relationship with his Norwegian girlfriend, not for revealing secrets.
After his release from prison in 2004, the Israeli authorities banned Mr Vanunu from speaking to foreign media and travelling abroad.
In 2007, Mr Vanunu was sentenced to six months in prison for breaking the conditions of his parole.