Britain's Foreign Secretary is confident a deal can be struck with Iran - a view not shared by a senior US official.
As negotiators from Iran and six world powers sit down for a second day of talks in Geneva they still face major hurdles if there is to be a breakthrough interim agreement on Tehran's nuclear programme.
Last night a senior American administration official here at the talks agreed progress had been made since the previous round of talks ended without success 10 days ago, but urged caution about the prospects of an agreement by Friday.
Speaking in Istanbul, British Foreign Secretary William Hague was more upbeat.
"The differences that remain between the parties are narrow and I believe that they can be bridged with political will and commitment," he said.
"So this is an historic opportunity to build agreement on how to curb nuclear proliferation in the Middle East and potentially to set our relations with Iran on a different path."
Iran insists on its right to enrich uranium despite numerous UN Resolutions calling on it to halt. The compromise on this could be that Iran stands by its claim, but does not insist other countries recognise that claim.
Another possible compromise could be for Iran to agree to stop enriching to levels close to weapon-grade material, but continue to enrich at lower levels.
The French would have to drop their insistence that Iran reduces its stockpile of uranium already enriched to the high level of 20%.
Perhaps the most difficult issue is Iran's plutonium reactor due to open next year.
It's thought France insists it must not open as that would be another route to a nuclear bomb, but Iran insists on its sovereign right to operate such a plant.
Here the compromise could be for France to agree the facility can open, and Iran to accept limits to what it can do within the facility.
If there is an agreement the US and EU will relax some of the sanctions currently hurting the Iranian economy. About $10bn belonging to Iran which is currently in foreign bank accounts would be unfrozen.
The talks are scheduled over three days ending tomorrow. However, in reality the negotiations have dragged on for 10 years. If there is no breakthrough the voices asking 'what is the point of continuing them' will grow louder.