A team of human rights experts from the United Nations has arrived in Iran - the first visit of its kind in seven years.
The United Nations working group will be in the country for nearly two weeks and will investigate allegations of illicit or arbitrary detention.
Their visit will include meetings with government officials and the judiciary and a trip to Tehran's notorious Evin prison.
It comes after last year's UN report accused the judiciary - dominated by conservatives - of bearing a heavy responsibility for the ongoing human rights violations.
'Situation serious'
The group consists of five independent experts from different countries and is headed by Louis Joinet of France.
Their 12-day visit will include meetings with officials from the ministries for foreign affairs, interior and justice.
The experts are also scheduled to meet magistrates, and representatives of the revolutionary courts, and visit prisons in Tehran, Isfahan, Shiraz and Jazd.
Last year, the UN report by the special rapporteur, Maurice Copithorne, who had been banned from visiting the country since 1996, said the judiciary was responsible for human rights violations.
Iran decided to invite the UN back in after a resolution was defeated last summer.
More groups, including one dealing with violence against women, will visit the country later this year.
Human rights groups have described the situation as serious, with no real signs of improvement.
Earlier this month, the European Commissioner for External Affairs, Chris Patten, visited Tehran to start negotiations on a trade and co-operation agreement.
He said if Iran was serious about engaging with the EU they must improve their human rights record, starting with a ban on stoning and an anti-torture bill.