TEHRAN — Nuclear talks between Iran and six world powers were “substantive and useful” and the parties will meet again on April 7-9, EU foreign policy chief Catherine Ashton said Wednesday.

“We had substantive and useful discussions covering a set of issues including (uranium) enrichment, the Arak reactor, civil nuclear cooperation and sanctions,” Ashton told reporters in Vienna.

Earlier in the day, senior Iranian negotiator Abbas Araqchi said that it was “too early to enter into negotiations for drafting a text for a final agreement.”

The Vienna gathering was the second in a series of meetings aimed at transforming a November interim deal into a lasting accord that resolves for good the decade-old standoff over Iran’s nuclear drive which the west suspects masks a military objective, despite repeated denials.

Under November’s interim deal with the United States, China, Russia, Britain, France and Germany, known as the P5+1, Tehran froze certain nuclear activities for six months in exchange for relief from punishing sanctions hitting its economy.

Under November’s agreement, Iran froze key parts of its nuclear program in return for minor sanctions relief and a promise of no new sanctions for six months.

Although it could be extended, the deal is currently due to expire on July 20.

In this Jan. 15, 2011 file photo, Iran's heavy water nuclear facility is back-dropped by mountains near the central city of Arak, Iran.  (AP Photo/ISNA, Hamid Foroutan)

In this Jan. 15, 2011 file photo, Iran’s heavy water nuclear facility is back-dropped by mountains near the central city of Arak, Iran. (AP Photo/ISNA, Hamid Foroutan)

The six powers now want Iran to reduce permanently — or at least for a long time — the scope of its nuclear activities in order to make it extremely difficult for Tehran to develop nuclear weapons.

A key issue still to be resolved is the future of the Arak heavy-water reactor, which Iran says will be used for research but which world powers say could provide Tehran with an alternative route to an atom bomb.

Araqchi reiterated that Iran would not shut down the reactor but said it could take measures to allay Western concerns over the nuclear facility.

“There is a room for discussion about the size and extent of the enrichment, considering Iran’s practical needs,” he said.

The negotiations which began on Tuesday were not affected by differences between Russia, the United States and other world powers over Ukraine, Araqchi was quoted as saying by ISNA news agency.

“The issue was not raised in the negotiations but it is normal that a crisis with such scope would overshadow other issues,” Araqchi said of the worst deterioration in East-West relations since the Cold War.