Powers seek concrete response from Iran on nuclear offer ALMATY (Reuters) - World powers urged Iran on Friday to give a "clear and concrete" response to their offer to ease some economic sanctions if Tehran stops its most sensitive nuclear work, in talks aimed at calming tensions that threaten to boil over into war. The six powers - the United States, Russia, China, France, Britain and Germany - met Iranian negotiators in the Kazakh city of Almaty at the start of the second round of talks this year, hoping to settle a decade-old row over Tehran's nuclear work. With an Iranian presidential election in June complicating decision-making in Tehran, there is little chance of a breakthrough, but Israel has indicated its patience with diplomacy is running out. Widely assumed to be the Middle East's only nuclear power, Israel has threatened to bomb Iran's nuclear facilities if Tehran does not curb the activities the world powers suspect are aimed at giving it the capability to make an atom bomb. Without a conclusive deal in sight, Western diplomats are hoping for at least a serious discussion of specific points of their proposal made at the last talks in February, including closing a nuclear facility and shipping some enriched uranium stockpiles abroad in return for easing some sanctions. "We are hoping the Iranian side will come back to us with a clear and concrete response ... to a fair and balanced proposal," Michael Mann, a spokesman for the six powers, told reporters as talks got under way in Kazakhstan's commercial hub. Iran has resisted pressure for years - despite hardening economic sanctions - arguing its uranium enrichment is for peaceful purposes only and therefore should be allowed to continue, under international law. Its negotiators arrived in Almaty with their own proposals, the Iranian media reported without giving any detail, and chief negotiator Saeed Jalili was defiant ahead of the talks. That is the acceptance of the rights of Iran, particularly the right to enrichment," Jalili said in a speech at an Almaty university on Thursday. World powers say, however, Tehran has relinquished that right by hiding its nuclear work from U.N. inspectors in the past and refusing to grant them full access. If talks fail to produce sufficient progress, Western governments are likely to impose new economic sanctions, with the double aim of pressuring Tehran while seeking to persuade Israel to hold back from any military action. Israeli Prime Minister Benjamin Netanyahu told visiting U.S. senators on Thursday that Tehran's nuclear work must be stopped. U.S. President Barack Obama sought to cool tempers during a trip to Israel in March, saying diplomacy was the best option, but he hinted at the possibility of last-resort military action. Experts say any response would not be immediate, as Iran will likely seek to keep diplomacy on track ahead of the election, in part to avert new sanctions, but without coming close to any deal. "The probable failure of this round (of talks) does not mean that (military) strikes are imminent or that diplomacy later this year has no chance," said Cliff Kupchan, Middle East director at the Eurasia consultancy. Obama's recent trip reassured Israel that Washington holds a tough position. In the best case, Western diplomats say, this could give the sides time to iron out details of any future deal. They won't be able to negotiate seriously until after the election ... They can get started, but they can't finish, " a senior U.S. official said on Wednesday before heading to Almaty. If Iran ... really engages in a negotiation, even if we all agreed today on the terms of an agreement, it would take time to put (it) together because this is a highly technical agreement. At the core of the six powers' concerns is Iran's enrichment of uranium to 20 percent fissile purity, a level that closes an important technological gap en route to making weapons-grade material. During the last meeting in Almaty the powers told Iran to stop producing such uranium, ship out most of its stockpile and shutter its Fordow facility, buried deep in a mountain near the city of Qom, where enrichment to 20 percent takes place. They sought to sweeten the deal with an offer to ease a ban on trade in gold and other precious metals and an import ban on Iranian petrochemical products. Additional reporting by Dan Williams in Jerusalem and Fredrik Dahl in Vienna; Editing by Alison Williams