Israeli ex-nuclear technician Mordechai Vanunu has been held for allegedly violating restrictions imposed after his release from prison in 2004.
Mordechai Vanunu says he has averted a nuclear holocaust in the region
Police said he was held at the al-Ram checkpoint north of Jerusalem as he was returning by bus from the West Bank.
The former nuclear scientist is barred from leaving Israel and is not allowed to visit the Palestinian territories.
He was jailed in 1986 for 18 years after discussing his work at the Dimona nuclear reactor with a UK newspaper.
"He (Mr Vanunu) has been taken to our International Crimes Unit for questioning," Israeli police spokesman Mickey Rosenfeld was quoted as saying by Reuters news agency.
Mr Vanunu flashed a victory sign before being taken away in a police vehicle.
Asked what he had done to prompt the arrest, he said: "Nothing. They just want to arrest me again. They don't want me to enjoy freedom."
Mr Vanunu served most of his jail term in solitary confinement.
He was released in April 2004 under strict conditions.
Mr Vanunu has not been allowed to have a passport, is forbidden to approach ports and airports, and is banned from talking to foreigners without permission.
Israel insists Mr Vanunu - who has converted to Christianity - still poses a security threat.
In March, he was charged with violating the terms of his release from jail by giving interviews to the foreign media.
Mr Vanunu says his action in revealing Israel's nuclear secrets aimed to avert a nuclear holocaust in the region.
Many Israelis view him as a traitor.