Talks between major powers and Iran are making progress but it is "painfully slow," British Foreign Secretary Philip Hammond said Friday, adding that ministers would reconvene in Vienna the following day.

"We're making progress, it's painfully slow ... there are still some issues that have to be resolved. I'm confident that our officials working with the Iranians over the next 12 hours or so will clear some more of the text and then we can re-group tomorrow (Saturday) to see if we can get over the last hurdles," Hammond told reporters in the Austrian capital.