Iranian Foreign Minister Mohammad Javad Zarif, right, welcomes European Union foreign policy chief Catherine Ashton to Tehran. (Vahid Salemi/AP)

The European Union’s foreign policy chief expressed optimism Sunday that world powers can reach a permanent deal with Iran over its nuclear ambitions, but she cautioned that success is far from certain.

“It’s difficult; it’s challenging. There’s no guarantee we’ll succeed. But I think it’s very important, with the support of the people of Iran, for the work that is going on by the minister and his team, and with the support of the international community for my work, that we should aim to try and succeed,” Catherine ­Ashton, the E.U.’s high representative for foreign affairs and security policy, said in a joint news conference with Iranian Foreign Minister Mohammad Javad Zarif.

Ashton is visiting Iran for the first time, meeting with top officials to discuss relations between Iran and the E.U. and issues of mutual concern, although the ongoing nuclear talks remain a priority for both parties.

In November, negotiators from Iran and the P5+1 group of countries — the United States, Russia, China, Britain, France and Germany — agreed to an initial deal that suspended some of Iran’s most sensitive enrichment activities in exchange for minor relief from sanctions that have wreaked havoc on Iran’s economy in recent years.

“I’ve been engaged in discussions with Iran for nearly four years on these issues, and I think this interim agreement is really, really important, but not as important as the comprehensive agreement we are currently engaged in,” Ashton said.

The next round of nuclear talks is scheduled to begin March 17 in ­Vienna.

Negotiations between Iran and the P5+1, which stalled several times in recent years, have gathered pace since August, when Hassan Rouhani took office as Iran’s president.

Western negotiators often expressed frustration with Saeed Jalili, who was their Iranian counterpart during much of Mahmoud ­Ahmadinejad’s presidency. Jalili was known for his deep resistance to making even limited concessions, and sanctions mounted on his watch.

But negotiations have been more fruitful since Rouhani took office, and the nuclear file was officially transferred from Iran’s national security team to its Foreign Ministry.

“Iran is determined to reach an agreement. We have shown good faith, we have shown political will, and as far as verification of our side of the bargain is concerned, we have done our side,” Zarif said at the news conference.

However, Zarif reiterated that Tehran can accept a deal only if it is “mutually acceptable” and acknowledges what his government contends is Iran’s right to a peaceful nuclear program.

“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,” he said.

Although Zarif said he thinks a permanent deal can be reached in a matter of months, both sides acknowledge the wide-ranging disagreements that must be addressed.

“Clearly, we want to negotiate quickly, but the most important thing is that it’s a good agreement that everyone can live with,” said Michael Mann, Ashton’s spokesman.

Ashton is the highest-ranking E.U. official to visit Iran since her predecessor, Javier Solana, was here in 2008.

“It’s important to come here and see what scope there is for working with Iran. We’ve done a lot of work with them on the nuclear file, but this is about much more than nuclear negotiations,” Mann said.

In addition to meetings with Rouhani and Zarif, Ashton met the speaker of Iran’s parliament, Ali Larijani.

Before leaving Iran, she is scheduled to travel to the central city of Isfahan to visit popular historical sites, according to Iranian news media.