Israeli Prime Minister Benjamin Netanyahu Sunday expressed concern Sunday at the progress of talks between world powers and Iran, saying that Tehran still sought to acquire a nuclear arms capability.

"Iran, in fact, is getting everything and giving virtually nothing," he told the cabinet on the eve of a visit by German Chancellor Angela Merkel, and said he would discuss the issue with her.

"I view with concern the fact that Iran believes that it will realise its plan to become a threshold nuclear state with an enrichment capacity that it thinks cannot be touched, with the ability to develop both nuclear weapons and inter-continental missiles, which it is continuing to work on unhindered," he said in remarks relayed by his office.

"This is the current situation. The permanent agreement cannot render this situation permanent. It must dismantle the Iranian ability to either produce or launch nuclear weapons," he added.

Germany -- with the United States, China, Russia, Britain and France -- is a member of the P5 + 1 group seeking to forge a lasting nuclear accord to resolve a decade-old stand-off over Iran's nuclear ambitions.

An op-ed piece by German Foreign Minister Frank-Walter Steinmeier published on Sunday in the top-selling Israeli daily Yediot Aharonot told Israelis: "You are not alone."

"The Iranian nuclear programme looms threateningly on the horizon," he wrote.

"The United States, Russia, China, Britain, France and Germany are debating in Vienna the future of Iran's nuclear programme. Our objective is clear: Iran must be prevented from acquiring nuclear arms."

Netanyahu's strategic affairs minister, Yuval Steinitz, on Sunday met Washington's chief negotiator at the Iran talks, Wendy Sherman, who briefed him on the negotiations, Israeli army radio said.

Briefing journalists in Jerusalem on Saturday night, Sherman said that nothing eventually agreed in the talks would be taken purely on trust.

"Nothing about this comprehensive agreement is about what we believe," a US State Department statement quoted her as saying.

"It is about what we see, what can be verified, what can be monitored, what are the concrete actions that will give us and the international community confidence in an exclusively peaceful nature of Iran's nuclear programme."