An Israeli nuclear whistleblower who spent 18 years in prison is going back to jail.

Mordechai Vanunu was taken into custody on Sunday for violating the conditions of his 2004 release, which include a ban on meeting foreigners. His lawyer says Vanunu has a Norwegian girlfriend.

The prison service says he is to serve three months.

Vanunu was a low-level technician at a nuclear plant who leaked details and pictures of the operation to the Sunday Times of London in 1986.

Foreign experts who reviewed the material concluded that Israel had a formidable nuclear arsenal.

Israeli intelligence agents kidnapped him in Rome and brought him back to Israel to stand trial.

Israel has never acknowledged or denied having nuclear weapons.