BRUSSELS/VIENNA - When world powers start talks with Iran next week on a final agreement on their nuclear dispute, the main question for the West will be how to ensure Tehran gives up enough atomic activity to ensure it cannot build a bomb any time soon.

If successful, the negotiations could put to rest a decade of hostility between the West and the Islamic Republic, and head off the danger of a new war in the Middle East.

Ingrained mistrust and a vast gap in expectations between the two sides may still doom the search for a deal: US President Barack Obama has put the chance of success at no more than 50 percent. Some say that is optimistic.

But both sides say the political will is there to reach what would amount to a historic compromise with potentially far-reaching geopolitical and economic consequences.

Iran holds some of the world's largest oil and gas reserves and with nearly 80 million people represents a largely untapped market with vast potential for foreign businesses.

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 suspend the most controversial aspect of its program - enrichment of uranium.

Diplomats privately acknowledge that Iran's nuclear work, which Western states fear may be aimed at developing the capability to assemble bombs, is now too far advanced for Tehran to agree to dismantle it completely.

But while Iran may be allowed to 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.

Iran says its nuclear programme is entirely peaceful.