A first phase of crucial talks between Iran and the International Atomic Energy Agency (IAEA) has ended in Tehran, with the Iranians optimistic about the outcome.
Iran's ambassador to the IAEA, Ali Akbar Salehi - who is in Tehran for the talks - told the BBC that agreement and mutual understanding had been reached on a plan of action to clarify the issues of concern to the agency.
The aim, he said, was to speed up co-operation, so that all the questions the IAEA is asking could be dealt with as swiftly as possible.
Dr Salehi said that there were no serious sticking points, but he cautioned that it was a dynamic process and he hoped that nothing unusual would come up.
The most senior IAEA official involved in the talks, deputy Director General Pierre Goldschmidt, has returned to Vienna, but other officials and tactical experts have stayed on.
They will be engaging in detailed discussions and some inspections as the agreed programmes of works gets under way.
So this first and crucial phase of talks has ended with the Iranians in an optimistic and positive mood.
On its side, the IAEA itself is being much more cautious.
In fact, it is saying virtually nothing at all.
Clearly much will depend on what actually happens in the coming days, and how forthcoming and convincing the Iranians turn out to be in meeting the agency's concerns.
These include questions about how traces of highly enriched weapons grade uranium came to found at two Iranian facilities.
By the end of the month the agency wants to have a full understanding of all Iran's past and present nuclear activities so that it is in a position to certify that the country has been abiding by its obligations under the Non Proliferation Treaty.
If it cannot do that, the issue may be referred to the United Nations Security Council where Iran could face sanctions.