Iran's chief negotiator in nuclear talks in Vienna warned Saturday that Tehran is ready to walk away if "excessive" Western demands cause a failure, a day before foreign ministers try to inject momentum.

Eight days before a deadline for a deal, Abbas Araqchi said however that he hoped that the attendance from Sunday of foreign ministers including US Secretary of State John Kerry would help overcome "deep differences" that remain.

"If we see that the excessive demands (of Western powers) persisting and that a deal is impossible, this is not a drama, we will continue with our nuclear programme," Araqchi said.

"The presence of ministers will have a positive influence," he told Iran state television from the Austrian capital. "There are questions that ministers need to take decisions on."

Iran's talks with the five permanent members of the UN Security Council plus Germany are aimed at a grand bargain reducing in scope Iran's nuclear activities in return for sanctions relief.

Such a deal is meant to quash for good concerns about the Islamic republic getting the bomb after more than a decade of failed diplomacy, threats of war and atomic expansion by Iran.

Iran denies wanting nuclear weapons. The deadline for an accord is July 20, when an interim accord struck by foreign ministers expires, although this can be put back if both sides agree.

Kerry was expected late Saturday or early Sunday in Vienna where he will be joined by his British, French and German counterparts William Hague, Laurent Fabius and Frank-Walter Steinmeier.

Hague said on Saturday that the Western ministers would also discuss how to achieve a ceasefire in Gaza. Kerry and Steinmeier were also to talk about a US-German spat over spying.

Skipping the meeting however is Russian Foreign Minister Sergei Lavrov, and it remains unclear who will represent China.

- Critical choices -

Kerry "will gauge the extent of Iran's willingness to commit to credible and verifiable steps that would back up its public statements about the peaceful nature of its nuclear programme," the State Department said.

He will "assess Iran's willingness to make a set of critical choices at the negotiating table" and then "make recommendations" to US President Barack Obama on the next steps.

Some progress has been made in drafting the actual deal, with Araqchi saying that both sides saw eye to eye on "60-65 percent" of issues.

But he added that there were still "deep differences" on the "fundamental issues".

The main problem area is uranium enrichment, a process which can produce nuclear fuel -- Iran's stated aim -- but also in highly purified form the core of an atomic weapon.

On Tuesday Ayatollah Ali Khamenei, Iran's supreme leader, gave a speech indicating that Tehran intends to greatly increase its enrichment capacities to fuel a future fleet of nuclear power stations.

The six powers want a sharp reduction, however.

This, coupled with increased surveillance, would extend the so-called "breakout time" -- the time Iran would need to make enough highly-enriched uranium for a nuclear weapon, if it choose to do so.

"We have made some progress but on some key issues, Iran has not moved from their ... unworkable and inadequate positions", a senior US official said Saturday.

"There is no question that we have heard about Iran's aspirations for its nuclear programme in very specific terms and very specific numbers, and that remains far from a significant reduction in their current programme."

Iran sees 'no benefit' in nuclear weapon: FM
Washington (AFP) July 12, 2014 - Iran's top diplomat Mohammad Javad Zarif says Tehran has no interest in building an atomic bomb, despite Western powers' claims otherwise.

Zarif's comments, in a television interview due to be broadcast Sunday, when Iran engages in talks with the five permanent members of the United Nations Security Council plus Germany aimed at a grand bargain reducing in scope the Islamic republic's nuclear activities in return for sanctions relief.

"I will commit to everything and anything that would provide credible assurances for the international community that Iran is not seeking nuclear weapons, because we are not," Zarif told NBC's "Meet the Press" from Vienna, where the talks are taking place.

"We don't see any benefit in Iran developing a nuclear weapon."

Zarif rejected "calculations" suggesting the Shiite country would seek to develop nuclear weapons to guard itself against its Shiite neighbors.

"We need to go out of our way in order to convince our neighbors that we want to live in peace and tranquility with them," he said.

"The politics of geography -- the fact that we're bigger, the fact that we're stronger, that we're more populous, the fact that we have a better technology, the fact that our human resources is by far more developed than most of our neighbors -- all of these provide us with inherent areas of strength that we don't need to augment with other capabilities."

Calling the principle of nuclear deterrence "simply mad," the foreign minister insisted that Pakistan was not considered stronger than Iran simply because it has nuclear weapons.

"The fact that everybody in the international community believes that mutual assured destruction -- that is the way the United States, Russia and others, seek peace and security through having the possibility of destroying each other 100 times over is simply mad," he added.

"I do not believe that you need to inculcate this mentality that nuclear weapons makes anybody safe. Have they made Pakistan safe? Have they made Israel safe? Have they made the United States safe? Have they made Russia safe? All these countries are susceptible," Zarif said.

"Now you have proof that nuclear weapons or no amount of military power makes you safe. So we need to live in a different paradigm. And that's what we are calling for."