“No agreement has yet been reached, but there has been substantial progress,” the news agency RIA Novosti quoted Russian Foreign Minister Sergey Lavrov as saying as he left the talks in Vienna.

The postponement means that Iran has won itself another seven months’ breathing space in which to carry on developing its program, in the face of western suspicions in that it wants to build a nuclear bomb. Teheran says it is only looking to use nuclear power in civil energy projects. The U.N.’s International Atomic Energy Agency says it hasn’t been able to confirm this.

The talks aimed to lay any doubts about Iran’s intentions to rest, in return for loosening the sanctions that have hamstrung its economy. Hopes for a deal had risen after the more moderate Hassan Rouhani replaced the hardline Mahmoud Ahmedinajad as Iran’s President last year.

Western nations agreed to relax sanctions against Iran in July in exchange for new limits on the program and an extension of talks on a final status agreement until this Monday.

Ministers will now resume negotiations next month and aim to wrap up a deal within three to four months, according to Britain’s Foreign Secretary Philip Hammond.

Hammond told the BBC that the failure to reach a deal was “a disappointment, but rather than continue blindly, we have to recognise the reality that we’re not going to make a deal tonight.”

With a final deal still pending, Iran will still be allowed to access $700 million a month in oil assets that were frozen under U.S. sanctions, the BBC reported.

The political backdrop in the Middle East has changed rapidly since the parties made a breakthrough on talks last year.

This year has seen Iran and the U.S. work together–if only informally–to combat the Sunni jihadi movement Islamic State in Iraq. However, any rapprochement between the two–and indeed, a broader deal on lifting sanctions–looks less likely after the Republicans took control of the Senate in mid-term elections earlier in November.