The European Union's foreign policy chief Catherine Ashton said on Wednesday, April 3 she is "cautiously optimistic" about nuclear talks with Iran in Kazakhstan on April 5-6, but said it was vital that Tehran responded to an offer put forward by major powers.

"I remain always cautiously optimistic. But I am also very clear that it is very important that we do get a response (from Iran)," Ashton told reporters in the Turkish capital when asked about the talks in Almaty, according to Reuters.