American and Israeli officials have differed over Iran's nuclear programme, as Israel called for its effective dismantlement and the US suggested safeguards could show that it was peaceful rather than military.
US Secretary of State John Kerry and Israeli Prime Minister Benjamin Netanyahu began talks on Wednesday in Italy, in what is intended to be about Israeli-Palestinian peace negotiations but appears to have been overshadowed by the Iranian issue.
Netanyahu called Iran's programme the region's foremost security problem.
We will need to know that actions are being taken which make it crystal clear, undeniably clear, fail-safe to the world that whatever programme is pursued is indeed a peaceful programme.
"Iran must not have a nuclear weapons capability, which means that they shouldn't have centrifuges (for) enrichment, they shouldn't have a plutonium heavy-water plant, which is used only for nuclear weapons," Netanyahu told reporters.
"They should get rid of (their amassed) fissile material, and they shouldn't have underground nuclear facilities, (which are) underground for one reason - for military purposes."
Iran has repeatedly stated it is enriching uranium solely for electricity and medical treatments, not nuclear weapons.
Kerry, who is exploring a diplomatic solution to rein in Iranian nuclear activity, took a different approach from Netanyahu by suggesting Iran could show its programme was peaceful by adhering to international standards followed by other nations.
"We will pursue a diplomatic initiative but with eyes wide open, aware that it will be vital for Iran to live up to the standards that other nations that have nuclear programmes live up to as they prove that those programmes are indeed peaceful," Kerry said.
"We will need to know that actions are being taken which make it crystal clear, undeniably clear, fail-safe to the world that whatever programme is pursued is indeed a peaceful programme."
Six global powers held talks with Iran last week in Geneva to test whether a diplomatic resolution might be reached, their first such negotiations since moderate Iranian President Hassan Rouhani's election in June opened up possibilities for a deal after years of increasing confrontation.
A second round of these talks, which include Britain, China, France, Germany, Russia and the United States, is scheduled for early November, also in Geneva.
|Western experts say demanding Iran ro halt all of its nuclear enrichment is not realistic [File: EPA]
Iran cites a right to refine uranium for peaceful purposes under the nuclear Non-Proliferation Treaty (NPT), a 1970 global pact to prevent the spread of nuclear arms.
But the US has said Iran does not automatically have this right under international law because, it argues, Tehran is in violation of its obligations under counter-proliferation safeguards.
A series of UN Security Council resolutions since 2006 has demanded that Iran suspend all enrichment and heavy water related activities.
But Western experts say, and some diplomats privately acknowledge, that it is no longer realistic to expect Iran to halt all its enrichment, as the Islamic state has sharply expanded this work in the last seven years and it is seen as a source of national pride and prestige.
Instead, they say, any deal should set strict, verifiable limits on the number of centrifuges that Iran can have and on the production of low-enriched uranium.