Israel "utterly rejects" a proposed deal on Iran's nuclear programme being hammered out in talks in Geneva, Prime Minister Benjamin Netanyahu said on Friday as he met Washington's top diplomat.

"This is a very bad deal. Israel utterly rejects it," he told reporters at Ben Gurion airport before beginning talks with US Secretary of State John Kerry, saying Iran was getting "the deal of the century."

Israel has been enraged by news emerging from Geneva where the so-called

P5+1 group of Britain, China, France, Russia, the United States plus Germany are meeting with Iranian officials for the latest round of talks over its controversial nuclear programme.

Officials have said a long-awaited deal on curbing Iran's nuclear ambitions may be finally within reach, after years of fruitless talks were given fresh momentum by the election of Iran's new President Hassan Rouhani, seen as a relative moderate.

"I understand that the Iranians are walking around very satisfied in

Geneva, as well they should be because they got everything and paid nothing," Netanyahu said, speaking as if a deal had already been done.

"They wanted relief of sanctions after years of a gruelling sanctions

regime, they got that, they are paying nothing because they are not reducing in any way their nuclear enrichment capability," he said.

"So Iran got the deal of the century and the international community got a bad deal, this is a very bad deal. Israel utterly rejects it," he said, stressing that the Jewish state would not see itself as bound by any such agreement.

"Israel is not obliged by this agreement and Israel will do everything it needs to do defend itself and the security of its people."

Israel, which has the Middle East's sole if undeclared nuclear arsenal,

sees a nuclear-armed Iran as an existential threat and has consistently refused to rule out a pre-emptive military strike to prevent that from happening.

Iran denies its nuclear programme has a military aspect, insisting on its sovereign right to enrich uranium, saying it is for peaceful civilian purposes only.