Six world powers (P5+1) - the United States, Britain, France, Germany, Russia and China - have agreed on relieving major UN sanctions against Iran if Tehran accepts the terms of a proposed nuclear deal, Reuters has reported.
The timing of the sanctions relief, access and verification of compliance and a mechanism for restoring sanctions - if Iran breaks its commitments - will be discussed in further negotiations.
According to US and European negotiating parties, the removed sanctions should be reversible in the event Tehran violates the agreement.
US and European negotiators want any easing of UN sanctions to be automatically reversible if Tehran violates the proposed deal. Russia and China traditionally reject the notion of such automatic measures as undermining their veto power as permanent members of the UN Security Council.
Officials involved in the negotiations did not disclose precisely how sanctions would be restored, but Western powers are adamant that it should be implementable without a Security Council vote, based on provisions to be included in a new UN Security Council resolution to be adopted after a deal is struck, a proposal preventing future interference by Russia and China, traditional allies of Iran
Iranian Foreign Minister Javad Zarif called on all countries to cease their nuclear weapons programs, emphasising the importance of ending the threat such weapons pose to humanity in late April.
“Any use or threat of use of nuclear weapons would constitute a crime against humanity and the continued existence of nuclear weapons poses the greatest threat to humanity," Zarif said at the beginning a month-long conference on the global nuclear weapons proliferation treaty.
"We call upon the nuclear-weapon states to immediately cease their plans to further invest in modernising and extending the lifespan of their nuclear weapons and related facilities," Zarif added.
The five permanent members of the UN Security Council - China, France, Russia, UK and the US - are officially known to possess nuclear weapons in accordance with the 1970 treaty on Non-Proliferation of Nuclear Weapons (the Nonproliferation Treaty or NPT in short), which is intended to stop the spread of nuclear weapons technology.
"We pretty much have a solid agreement between the six on the snapback mechanism, Russians and Chinese included," a Western official said. "But now the Iranians need to agree".
If a snapback mechanism is accepted by Iran, more steps will follow such as the access of International Atomic Energy Agency (IAEA) to Iranian military sites and nuclear scientists.
Rejecting allegations from Western countries, Iran claims its nuclear program is entirely peaceful and intended to meet energy needs.
In a 2007 National Intelligence Estimate, the United States Intelligence Community assessed that Iran had ended all "nuclear weapon design and weaponization work" in 2003.
In 2012, US intelligence agencies reported that Iran was pursuing research that could enable it to produce nuclear weapons, but was not attempting to do so.
Following the report, the P5+1 powers sped up nuclear talks with Iran.
After the conclusion of negotiations, Iran expects the UN to initially lift the latest, most damaging, sanctions.