Catherine Ashton was in Tehran for meetings with Iranian officials on ongoing negotiations over the country's nuclear program, as well as the civil war in Syria and other issues. She spoke to reporters in a joint briefing with Iran's foreign minister Mohammad Javad Zarif.
Separately, Iran's President Hassan Rohani advocated pursuing "new relations" with European countries that for years have been at odds, alongside the United States, with Tehran over Iran's disputed nuclear program.
"Besides ongoing nuclear talks that should be driven ahead, there are other suitable fields in which both Iran and European Union can consider and push relations and cooperation ahead," the president said in remarks quoted by his website. He suggested energy and transportation cooperation.
Under an interim deal in November, Iran agreed to limit a key nuclear activity, uranium enrichment, in return for easing sanctions by the West.
Negotiations for a final deal are ongoing. Ashton leads the six-nation group — the U.S., Britain, France, Russia, China and Germany — in talks with Iran.
"I think this interim agreement is really important, but not as important as the comprehensive agreement that we are currently engaged in. Difficult, challenging, there's no guarantee we'll succeed," she said.
Zarif said Iran will only accept a deal that respects its "rights," a reference to uranium enrichment on its soil, while reiterating Iran's longstanding position that his country is not pursuing nuclear arms.
"Iran will only accept a solution that is respectful, that respects the rights of the Iranian people," he said.
"At the same time, Iran finds it in its own interest to make sure that there are no ambiguities about Iran's intentions, because we have no intention to seek nuclear weapons."
The two said they had also discussed fighting terrorism, drug trafficking, and conflicts in Afghanistan and Syria. Iran is a key ally of Syrian President Bashar Assad.
Under the historic deal, Iran agreed to halt its 20 percent enrichment program, but will continue enrichment up to 5 percent. It also will convert half of its stockpile of 20 percent enriched uranium to oxide, and dilute the remaining half to 5 percent. Enrichment to 20 percent is a possible pathway to nuclear arms.
The West suspects Iran's nuclear program has a military dimension. Iran denies the charge, saying its nuclear activities are aimed at peaceful purposes like power generation and medical treatment.
Earlier on Sunday, Prime Minister Benjamin Netanyahu lashed out at Ashton, who was visiting Iran on a landmark visit, just days after Israel raided an Iranian ship carrying missiles bound for Gaza.
"The goal of seizing the arms ship was to expose Iran's true face," Netanyahu told ministers at the weekly cabinet meeting in Jerusalem. "I say this in order to bring it to the attention of Ms. Ashton, who is now visiting Tehran, and I wish to ask her whether she asked her hosts about the shipment of weapons to terrorist organizations."
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