Israeli nuclear whistleblower Mordechai Vanunu would be a “prisoner of conscience” if Jerusalem authorities pursue new charges against him, Amnesty International has said.

The human rights group, which criticised Israel over the 2014 Gaza conflict, said it would campaign for him after Jerusalem Magistrate’s Court charged him on 8 May.

The charges relate to a meeting he held with two American nationals three years ago, an interview he gave to Israeli broadcaster Channel 2 last year, and for not correctly informing the authorities about his house move within Israel.

“If Vanunu is convicted and imprisoned under the new charges, Amnesty would consider him a prisoner of conscience held solely for peacefully exercising his right to freedom of expression, and the organisation would call for his immediate and unconditional release,” an Amnesty statement read.

Avigdor Feldman, the lawyer acting for Vanunu, said the charges were “a record low” for the state “in its persecution and abuse of Mordechai Vanunu,” adding: “I’m ashamed, and whoever filed this indictment should be even more ashamed.”

Vanunu gave details of Israel’s nuclear programme to The Sunday Times for which he was jailed for 18 years in 1986. He spent more than a decade of his jail term in solitary confinement, considered to be a form of psychological torture.

He was released under strict terms in 2004 and has since been banned from leaving the country, talking to journalists or foreign nationals, approaching or entering national embassies and using the internet.

However, right-wing groups have continued to deride him as a traitor who sold secrets, and Gerald Steinberg, head of NGO Monitor, whose funding is unclear, said this week of Vanunu that “the term ‘whistle-blower’ is clearly out of place”.

He added: “Amnesty has a long and sad record of anti-Israel campaigning, and has no moral standing to make accusations or condemn the decisions of the elected Israeli government.”