Stefan de Rynck, a Commission spokesman, said the EU expects Iran to live up to the so-called Paris agreement, struck last fall between Iran and Britain, France, and Germany.
The EU interprets the agreement as committing Iran to suspend indefinitely all enrichment-related activities in exchange for an EU aid package and a promise of closer political and security ties.
De Rynck said today that the commission hoped negotiations with Iran could still produce a result.
"The commission very much hopes for a negotiated solution to come forward," de Rynck said. "We would also hope that no steps will be taken over the coming days that would endanger such a negotiated solution."
Another EU official said today that Britain, France, and Germany would unveil details of the aid package in a week.
Iran initially demanded the proposals by 31 July but extended the deadline by one day. According to news agencies, Tehran today handed over a letter to the International Atomic Energy Agency in Vienna, Austria, which “touches upon” uranium conversion.
Yesterday Britain, which currently chairs the EU, urged Iran to avoid unilateral steps that it said would make it “very difficult” to continue the talks with the EU.
France and Germany have also expressed concern.
Earlier, the United States said it supports the EU-Iranian talks. Washington has also indicated it could offer incentives of its own, such as unblocking Iran’s bid to join the World Trade Organization (WTO).
It is believed that U.S. support was secured by Britain, France, and Germany in return for a commitment to refer Iran to the UN Security Council should Iran resume enrichment-related work.
The European Commission also warned today that resumption of nuclear activity could lead to a suspension of the twin-track trade and political talks that the commission is conducting separately with Tehran.
"Progress on such an agreement is unlikely unless the favorable climate which has been created by France, Germany, and the U.K. and their Iranian counterparts to the Paris agreement has a successful follow-up," dy Rynck said.
The talks are intended by Brussels to lead to the signing of parallel agreements facilitating trade and political ties.