No date has been set for the deal between six world powers and Iran to take effect, and talks on implementing it ran into trouble last week when the United States blacklisted additional Iranian companies and people.
Under the accord, Iran is supposed to suspend its most sensitive nuclear work while governments in the United States and Europe ease some economic restrictions, in a first step towards a comprehensive settlement of the decade-old dispute.
The sequence of lifting sanctions and Iran's nuclear steps has been an issue in discussions between Iran and the six powers - the United States, Russia, China, France, Britain and Germany.
The International Atomic Energy Agency (IAEA), a UN body, is expected to verify that Iran has taken the agreed steps.
In a statement, EU foreign ministers said Iran had to implement its side of the deal in good faith.
"For its part, the Council is committed to ... suspend those EU sanctions as set out in the (agreement) immediately after the IAEA has verified the implementation of the nuclear-related measures by Iran," they said.
Western nations imposed sanctions on Iran over its nuclear program. Tehran says its nuclear drive is only for peaceful purposes.
Iran's Deputy Foreign Minister Abbas Araqchi travelled to Brussels on Monday to meet EU foreign policy chief Catherine Ashton, who oversees contacts with Iran for the six nations, to discuss implementation of the nuclear deal.
Ashton said the meeting, scheduled for Tuesday, was requested by Iran, and she hoped discussions would resume quickly between teams of experts from both sides on how and when to roll out last month's deal.
"I gather that he is coming with some messages for me from Foreign Minister (Mohammad Javad) Zarif," she told reporters.
"I am expecting us to move forward to agree on the implementation timetable as soon as possible. The ambition we have is to have a date agreed that is achievable."
Britain's Foreign Secretary William Hague also said that these discussions could take time.
"While we have reached the interim deal, the details of implementation remain to be negotiated and there will be many difficulties in that, so we shouldn't be surprised if these talks are difficult," he told reporters.
Hague also said Western governments would keep up economic pressure on Iran.
"We have to maintain our vigilance on sanctions and maintain the sanctions that we are not suspending so that Iran has a clear incentive to make a comprehensive deal," he said.
Scope for diplomacy widened after Iran elected the pragmatic Hassan Rouhani as president in June, and he promised to reduce Tehran's isolation and get sanctions eased. But after years of mutual distrust any progress will likely be fragile.
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