By Miranda Eeles
BBC correspondent in Tehran
A team of United Nations human rights experts has concluded a visit to Iran noting serious shortcomings in the country's justice system.
Louis Joinet criticised Iran's justice system
The Working Group on Arbitrary Detention met officials and members of the judiciary and visited Tehran's notorious Evin prison, where they met several political prisoners.
The leader of the group - French magistrate Louis Joinet - together with four independent experts were in Iran to investigate allegations of illicit or arbitrary punishment and the workings of the justice system.
They met more than 100 prisoners and several political detainees.
They also visited a number of prisons, including one of the unofficial detention centres.
The group believes that full solitary detention [is] practised on a large scale and for very long periods
Working group leader
Speaking at a press conference at the end of the visit, Mr Joinet said that major problems do remain, particularly regarding political prisoners in isolation.
"The group believes that full solitary detention [is] practised on a large scale and for very long periods," he said.
Mr Joinet described a justice system where there was an absence of a lawyer culture and therefore a defence culture.
He also spoke of sentences that were quite disproportionate with the nature of the crimes committed and that there was not so much a problem of freedom of expression, rather than of a freedom after expression.
This is the first time in seven years that a team from the office of the UN High Commissioner for Human Rights has been allowed to visit Iran.
Last year a UN report accused the judiciary, which is dominated by conservatives, of bearing a heavy responsibility for the ongoing violation of human rights.
The visit by the experts has not passed without some controversy.
For three days, crowds gathered outside their Tehran hotel, protesting against the detention of political prisoners.
According to reports, security forces arrested several of the demonstrators.