Iran, US agree final nuclear deal may be unreachable

CURBING URANIUM ENRICHMENT

US to deal harshly with violators of Iran sanctions Iran ready for long term deal: FM

The goal of the talks for the United States and its European allies is to extend the "breakout time" that Iran would need to produce enough fissile material for a bomb.

For that goal to be achieved, experts and diplomats say, Iran would have to restrict enriching uranium to a low fissile concentration, stop most of its centrifuges now used for such work, limit nuclear research, and submit to highly intrusive monitoring by UN inspectors.

Khamenei and other Iranian officials have repeatedly made clear that such reductions of its nuclear capacities would be unacceptable.

Western governments appear to have given up on the idea, enshrined in a series of United Nations Security Council resolutions since 2006, that Iran should halt entirely the most controversial aspects of its programme - all activities related to the enrichment of uranium and production of plutonium.

Diplomats privately acknowledge that Iran's nuclear work is now too far advanced for Tehran to agree to dismantle it completely.

But while Iran may keep a limited enrichment capacity, the West will seek guarantees that mean any attempt to build a nuclear bomb would take long enough for it to be detected and stopped, possibly with military action.

The talks in Vienna begin on Tuesday and are expected to last for several days. Senior officials from the six powers will meet with an Iranian delegation led by Foreign Minister Mohammad Javad Zarif and his deputy Abbas Araqchi.

European Union foreign policy chief Catherine Ashton coordinates the negotiations on behalf of the six powers. The talks will be the first in what is expected to be a series of meetings in the coming months.

While cautioning the talks would take time, the US official said Washington does not want them to run beyond a six-month deadline agreed in the November deal. The late July deadline can be extended for another half year by mutual consent.