The UN secretary general, Ban Ki-moon, has sharply rebuked the Iranian president, Hassan Rouhani, for failing to improve human rights since taking office in August.

Despite "commendable steps" under Rouhani, including the release of a limited number of high-profile political prisoners, violations had continued, Ban reports in a new report to the UN human rights council issued on Tuesday.

Execution, arbitrary detention and unfair trials, descrimination against minorities, mistreatment of political prisoners, and restrictions on freedom of expression, are among subjects that remain concerns, according to Ban.

The secretary general said he was particularly concerned about the increased use of capital punishment in Iran.

"At least 500 persons are known to have been executed in 2013, including 57 in public. According to some sources, the figure may be as high as 625. Those executed reportedly included 27 women and two children," Ban said.

Ahmed Shaheed, the UN special rapporteur for human rights in Iran, said on Wednesday that, in Iran, at least 176 people so far had been put to death this year alone.

Ban complained that Iran had not allowed Shaheed to visit and investigate the abuse claims on the ground.

Ban said: "The new government has not changed its approach regarding the application of the death penalty and seems to have followed the practice of previous administrations, which relied heavily on the death penalty to combat crime."

His report also urged Rouhani to consider the immediate release of the two opposition leaders, Mir Hossein Mousavi and Mehdi Karroubi, who have been under house arrest without trial since the aftermath of the 2009 presidential election, won by the hardline Mahmoud Ahmadinejad.

Ban said that at least 80 political prisoners had been released since mid-September, including the prominent human rights lawyer Nasrin Sotoudeh, but that many remained in jail.

"Despite these welcome developments a large number of political prisoners, including high-profile lawyers, human rights activists, women rights activists and journalists, continue to serve sentences for charges that are believed to be linked to the exercise of their freedoms of expression, association and peaceful assembly."

Lawyers including Abdol Fattah Soltani, Mohammad Ali Dadkhah, and Mohammad Seifzadeh, were "detained solely for exercising their rights to freedoms of expression, association and assembly", according to the report.

Ban said that Rouhani's administration had not made "any significant improvement in the promotion and protection of freedom of expression and opinion" despite pledges made by the president during his campaign and after his swearing-in.

At least 35 journalists were also held behind bars, and two newspapers had been shut down recently.

"Both offline and online outlets continue to face restrictions including closure," the secretary general said.

On freedom of belief, he warned: "Religious minorities such as Baha'ís and Christians face violations entrenched in law and in practice. Harassment, home raids and incitement to hatred, are reportedly commonly applied by the authorities to suppress the Baha'i community."

Apart from Ban, the EU foreign policy chief, Catherine Ashton, has also raised concerns about the situation of human rights in Iran. Ashton infuriated Iranian hardliners when she met a number of women's rights activists during a recent visit to Tehran.

On Wednesday Ashton's meeting was still creating ripples in Iran, with the head of the judiciary and parliament condemning it.