Catherine Ashton has infuriated hardliners in Tehran by meeting a group of leading women's rights activists during her first visit to Iran as EU foreign policy chief.

Ashton, who brokered a historic interim nuclear agreement with Iran last year, met six female activists at the Austrian embassy in Tehran on Saturday, marking International Women's Day just hours after arriving in the Iranian capital. Ashton took the helm as the EU high representative for foreign affairs in 2009.

"The main purpose of the visit was to, as EU high representative, have a chance to talk to Iran about the potential for the relationship that we can have in the future," Ashton said on Sunday.

"Not surprisingly, there was a big focus on human rights: I met with women activists on International Women's Day and talked to them about the situation that women find themselves in and some of the work that these women are engaged in, from journalists to those involved with Afghan refugees, people working across the spectrum of civil society and the importance of civil society."

Iran's foreign ministry protested to the Austrian embassy on Monday, saying Ashton's meeting was unsanctioned. The spokeswoman, Marzieh Afkham, also accused the EU of double standards on human rights, local media reported. "Such actions will increase the suspicion of our citizens towards the west," the spokeswoman said. "This will not help our relations with Europe."

At least two Iranian MPs said Ashton was interfering in Iran's internal affairs.

Ashton's spokesman, Michael Mann, brushed off criticism, telling the Guardian human rights remains "a key and crucial part" of EU's foreign policy with Iran.

Narges Mohammadi, who has been sentenced to six years in jail for acting as the deputy head of Iran's Defenders of Human Rights Centre (DHRC), was one of the six Iranians who received an invitation from Ashton for the meeting, she told the Guardian on the phone from Tehran.

Ashton also met Gohar Eshghi, the mother of an Iranian blogger who died in custody while having no access to his family or lawyer. Eshghi has since become active pursuing what she calls a "just" trial of the people involved in the death of her son, Sattar Beheshti.

"Ashton wept as she embraced Eshghi, I was absolutely touched," said Mohammadi. "Ashton told Eshghi that as a mother herself she can completely understand how it feels to lose a child like that."

Ashton's visit to Iran came a few weeks after Tehran and six world powers including Britain, France, Germany, China, Russia and the US – the group known as P5+1 – started negotiations in Vienna aimed at reaching a comprehensive agreement that could potentially settle the decades-long dispute over the Islamic republic's nuclear programme.

Ashton also met Iran's president, Hassan Rouhani, and foreign minister, Mohammad Javad Zarif.

"The interim agreement is really important but not as important as a comprehensive nuclear agreement … which is difficult and challenging," Ashton said in a joint press conference with Zarif on Sunday. "There is no guarantee [negotiations] will succeed."

Zarif, on the other hand, said Iran was determined to reach an agreement, which he said could happen within four to five months.

Rouhani's election last year has increased hope for an improvement in women's rights in Iran but Mohammadi said it was too early to say if he will succeed in delivering his promises.

"People are certainly more hopeful but many of the restrictions are still in place," Mohammadi said. "There's a security atmosphere and women's activists are still being sentenced to jail."

Last week, a Tehran court sentenced the student activist Maryam Shafipour to seven years in prison for peaceful activism.

According to Mohammadi, at least 14 women's rights campaigners are locked up in Tehran's Evin prison, including Bahareh Hedayat, a student activist sentenced to nearly 10 years in prison.

"At almost 32, Bahareh has already spent over four-and-a-half years in prison," said Sussan Tahmasebi, an Iranian women's rights campaigner. "Bahareh's charges are in relation to her activities as a student rights defender, and as a women's rights defender. She has worked tirelessly to advocate for the right of students to organise in universities, to select their own university dean, to ensure that good educators are not dismissed."

The circumstances surrounding Beheshti's death are still unclear. He was 35 and from a lower-class family and dabbled in blogging and spoke out about human rights violations in his country. Unable to silence him online, Iran's cyber-police, known as Fata, picked him up from his home in 2012 and a week later his family received a phone call to collect his dead body.

In December, a Tehran court closed the case investigating his death, saying he had died of a "quasi-murder" but not charging any of his interrogators, according to the International Campaign for Human Rights in Iran.

"In a medical report that is part of the case, it is written that Sattar suffered from haemorrhaging in his liver, lungs and cerebellum, keeping oxygen from reaching the different parts of his body, and has slowly died," Beheshti's mother has told the campaign.

"Some hard days went by for us. They didn't let me see my son's face before his burial. I only saw that they put him in the grave wrapped in a bloody shroud. We were repeatedly threatened and verbally abused. I passed all those days because I was hopeful my son's murderer would be prosecuted. But now I see that the murder charge has been lifted."

Ashton's visit to Iran has provoked criticism in Israel. "I'd like to ask her if she asked her Iranian hosts about the delivery of weapons to the terror groups, and if she didn't, why not?" asked Israel's prime minister, Binjamin Netanyahu, invoking the recent seizure of an allegedly Iranian missile shipment "destined for Gaza".