Israel's top court has ordered nuclear whistleblower Mordechai Vanunu back to jail for three months after he refused to do community service in west Jerusalem for fear of harassment.

After having already served 18 years behind bars, a Jerusalem court convicted Vanunu and sentenced him to three months in jail or community service for meeting with a foreigner in violation of the terms of his release.

Vanunu asked the supreme court if he could perform the community service in Arab east Jerusalem, saying he feared he would be "harassed by the Israeli population" in the west of the city.

The supreme court rejected the argument, saying suitable work had been found in mainly Jewish west Jerusalem.

"The plaintiff refused and the court had no choice but to sentence him to three months in jail, which he will serve starting May 23," it said in a ruling issued on Tuesday.

Rights group Amnesty International to urge Israel not to re-imprison Vanunu.

"If Mordechai Vanunu is imprisoned again, Amnesty International will declare him to be a prisoner of conscience and call for his immediate and unconditional release," deputy director for the Middle East and North Africa Philip Luther said in a statement.

"The ongoing restrictions placed on Mordechai Vanunu have meant that he has been unable to move to the USA to live with his adopted family, placing a huge strain on his mental and physical health," Luther said.

"They are not parole restrictions since he served his full 18-year term. They arbitrarily limit his rights to freedom of movement, expression and association (and) are therefore in breach of international law."

Vanunu was jailed in 1986 for disclosing the inner workings of Israel's Dimona nuclear plant to Britain's Sunday Times newspaper.

Since his release in 2004, he has been detained several times for violating the terms of his release that ban him from travel or contact with foreigners.

Israel is widely believed to be the only nuclear power in the Middle East, with around 200 nuclear warheads, but has a policy of neither confirming nor denying that.

The Jewish state has refused to sign the nuclear Non-Proliferation Treaty or allow international surveillance of Dimona in the southern Negev desert.

Vanunu became an international cause celebre during his time in prison.

At home, he is still widely reviled for converting to Christianity shortly before he was kidnapped in Italy and jailed after being covertly shipped back to the Jewish state.