Tehran: Iran nuclear talks entered Thursday the decisive, dangerous endgame with a final round of hardball negotiations potentially going all the way to a July 20 finish line.
The deal being sought by Iran and the five permanent members of the UN Security Council plus Germany would finally ease fears of Tehran getting nuclear weapons and silence talk of war, in exchange for ending punishing sanctions on the Islamic republic.
With Sunni Islamic insurgents overrunning large parts of Iraq and Syria in chaos after years of civil war, this could help Tehran and the West normalise relations at an explosive time in the Middle East.
"In this troubled world, the chance does not often arise to reach an agreement peacefully that will meet the essential and publicly expressed needs of all sides, make the world safer, ease regional tensions and enable greater prosperity," US Secretary of State John Kerry said this week.
In a Washington Post tribune, he warned Iran not to "squander a historic opportunity to end Iran`s economic and diplomatic isolation and improve the lives of their people".
The P5+1 powers have proposed a "series of reasonable, verifiable and easily achievable measures that would ensure Iran cannot obtain a nuclear weapon and that its program is limited to peaceful purpose," he said.
"What will Iran choose? Despite many months of discussion, we don`t know yet."
Iranian Foreign Minister Mohammad Javad Zarif, in a video message, called the talks a "unique opportunity to make history", saying success would allow both sides to address "common challenges" such as Iraq.But with major differences apparent after five rounds of talks seeking to secure a deal by July 20 -- when an interim deal from November expires -- Zarif said in French daily Le Monde that some among the P5+1 were suffering from "illusions".
The United States, Russia, China, Britain, France and Germany want Iran to reduce drastically in scope its nuclear activities in order to render any Iranian drive to assemble a weapon all but impossible.
This would include in particular Iran slashing its capacities to enrich uranium, a process that produces nuclear fuel but also, at high purities, the core of a nuclear weapon.
In itself, that would represent a concession to Iran, which is defying six UN Security Council resolutions ordering it cease all enrichment.
But Iran insists it has made too many advances in uranium enrichment to turn the clock back. It rejects any need to cut its number of centrifuges and says it even needs to expand their number to fuel a fleet of future nuclear power plants -- facilities that it would be decades away from having.
Demands that Iran`s programme be "radically curbed" rest on a "gross misrepresentation of the steps, time and dangers of a dash for the bomb", Zarif said.
He said Iran "will not abandon or make a mockery of our technological advances or our scientists".
Iranian negotiator Majid Takhte Ravanchi said Iran "will not accept definitive restrictions" on its nuclear programme.
"If (the other side) have a maximalist position ... there will be no deal," he said.In theory, the July 20 deadline could be extended by up to another six months, and many analysts believe this is already being discussed.
But US President Barack Obama, facing midterm elections in November and Republican accusations of weakness, is wary of doing anything that could be construed as giving Iran more time to get closer to having the bomb.
This is the long-standing accusation of Israel, the Middle East`s sole if undeclared nuclear-armed state which -- together with Washington -- has not ruled out military action on the Islamic republic.
But Kelsey Davenport from the Arms Control Association believes that Washington should not shy away from pushing back the deadline if Iran is "negotiating in good faith".
"The alternative to no deal is far worse for the international community," she told AFP.