Israel urged world powers on Wednesday to reject what it said was an Iranian offer to partly cut back its nuclear programme in return for an easing of Western sanctions.
"Israel in the last few hours has learned that a proposal will be brought before the P5+1 in Geneva in which Iran will cease all enrichment at 20 percent and slow down work on the heavy water reactor in Arak, and will receive in return the easing of sanctions," an official told AFP on condition of anonymity.
"Israel thinks this is a bad deal and will oppose it strongly," the official said.
The so-called P5+1 group of major powers will meet Iran's nuclear team in Geneva on Thursday and Friday for the latest round of negotiations revived after the June election of Iranian President Hassan Rouhani, a reputed moderate.
Iran's enrichment of uranium to 20 percent has been a particular source of concern for the West as it is seen as a key step on the way to the 90 percent plus level required for a nuclear weapon.
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The heavy water reactor under construction at Arak is also a source of concern as it would provide a source of plutonium, an alternative route to a nuclear warhead.
A senior US administration official said Wednesday that Washington was willing to offer Iran limited sanctions relief if it agreed to take an unspecified "first step" to stop advancing its nuclear programme.
"Israel's assessment is that the P5+1 is in a position of strength. The sanctions are hurting Iran, Iran is feeling the pressure and the P5+1 has the capability to compel Iran to end all enrichment and to stop construction of the facility in Arak," the Israeli official said.
The P5+1 includes the five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- plus Germany.
The group has held years of talks with Tehran on its nuclear programme, which Western governments suspect may be cover for a drive for a weapons capability.
Iran has repeatedly denied any such ambition, insisting its nuclear programme is solely for generating electricity and for medical purposes.