Israeli Prime Minister Benjamin Netanyahu said on Tuesday nothing short of Iran stopping uranium enrichment, getting rid of what it already produced and dismantling the means of making more, would satisfy him that it had no nuclear weapons project.
"This is the true test. Without that there is nothing," he told a strategic affairs conference in Tel Aviv.
He said the six world powers, which last week finished a second round of negotiations with Iran over its disputed nuclear programme and scheduled the next meeting in Moscow on June 18-19, needed to take a tougher stance.
"Not only do they need to strengthen the sanctions, they need to strengthen their demands from Iran for which they have placed the sanctions," the right-wing Israeli leader said.
He reiterated his demands that along with a total halt to enrichment, Iran must also remove all nuclear material already enriched from its territory and dismantle the bunkered nuclear facility near the city of Qom.
"Only a clear Iranian commitment to fulfill those three demands and explicit verification that it has been done can stop Iran's nuclear programme. That needs to be the aim of the negotiations," he said.
Many analysts and diplomats believe no deal will be possible in the near future unless both sides compromise.
One mooted formula would require Iran to stop enriching uranium to higher grades to ensure no bomb material is produced, and accepting more intrusive U.N. inspections, in exchange for an easing of punitive sanctions.
Earlier on Tuesday, a senior Israeli official said the talks last week in Baghdad between the six powers and Iran had achieved nothing. Vice Prime Minister Moshe Yaalon said Baghdad had only produced "more Iranian time-buying".
"(There was) no significant achievement except for the Iranians having been given another three weeks or so to pursue the nuclear project until the next meeting in Moscow," he told Israel's Army Radio in an interview.
"To my regret, I don't see any sense of urgency, and perhaps it is even in the interest of some players in the West to stretch out the time, which would certainly square with the Iranian interest."
FROM MEETING TO MEETING
Like Israel, Washington says military action could be a last option against the Iranians, who deny seeking the bomb and have vowed to fight back on several fronts if attacked.
Washington has sought to reassure the Netanyahu government that potentially productive talks have not yet been exhausted.
The Baghdad meeting focused on foreign efforts to roll back Iran's enrichment of uranium to 20 percent fissile purity, a level approaching bomb grade. Iran says the higher-grade enrichment is for fuel to run a medical research reactor.
Netanyahu said the original red line had been set at 3.5 percent enrichment - sufficient to run civilian nuclear power stations - but had been relaxed.
"Even when faced with lesser demands, the Iranians have yet to respond positively," Yaalon said. Sanctions should be toughened, he said, but "we have not even reached that stage in the talks. Instead, we roll the matter from meeting to meeting".
Asked if the June 18-19 Moscow talks might prove conclusive, Yaalon said: "Let's hope. ...The Iranians are working to buy time, to hoodwink the Western world and to continue spinning (uranium) centrifuges toward a military capability."
Iran says it is stockpiling enriched uranium only for a future network of nuclear power plants and to make isotopes for cancer treatments.
Though Israel is reputed to have the Middle East's only atomic arsenal, many international experts, including the top U.S. military officer, General Martin Dempsey, have voiced doubt in the ability of its conventional forces to deliver lasting damage to Iran's dispersed and well-defended nuclear facilities.
That has given rise to speculation that Israel is involved in a recent rash of anti-Iran sabotage, including cyber-warfare.
A new computer virus, dubbed Flame, emerged on Monday, with analysts saying it may have been built on behalf of the same nation that commissioned the unclaimed Stuxnet worm that struck Iran's nuclear programme in 2010.
Asked if such assessments were sound, Yaalon, a former Israeli spymaster and military chief, said: "Apparently."
(Additional reporting by Dan Williams and Ari Rabinovitch; Editing by Crispian Balmer and Mark Heinrich)