"I have urged the authorities during my visit this time to release opposition leaders, human rights defenders, journalists and social activists to create the conditions for free expression and open debate," Ban said, according to the text of the address delivered late Thursday to an Iranian diplomats' college.

Ban said that allowing the Iranian people's voice to be heard was especially important ahead of the country's 2013 presidential election, when a successor to President Mahmoud Ahmadinejad will be chosen.

"Restricting freedom of expression and suppressing social activism will only set back development and plant the seeds of instability," Ban warned.

The last presidential election in Iran in 2009, which saw Ahmadinejad declared the winner amid allegations by his challengers of fraud, was followed by widespread protests that were brutally crushed by authorities.

The figureheads of the opposition "Green Movement" have languished under house arrest ever since.

Iranian officials gave no immediate reaction to Ban's speech.

A brief state television report on the address referred only to the very last part of Ban's speech, in which he thanked Iran for giving him a Persian carpet as a gift.

Elsewhere in his speech, Ban expanded on points he presented at the opening of the two-day NAM summit in Tehran, especially warning Iran it faced isolation if it did not comply with UN resolutions demanding it curb its nuclear programme.

Stressing "the cost of Iran's current trajectory," he said that "any country at odds with the international community is one that denies itself much-needed investment and finds itself isolated from the thrust of common progress."

Returning to Iran's human rights record and repression of political dissidents, he said: "Any country at odds with itself deprives itself of its people's energy and goodwill, and sets the stage for future instability."

The people were killed in rioting between Hindu and Muslims in the Naroda Patiya area of Ahmedabad city after a fire aboard the Sabarmati Express train in February 2002.

Fire erupted in two carriages of the train while it was at Godhra station about 80 miles from Ahmedabad and 58 Hindu pilgrims, including 27 women and 10 children, died in the fire.

The controversial incident, known as the Godhra Train Fire, set off communal rioting around Ahmedabad and other areas of Gujarat that lasted until June. Up to 1,200 people -- Muslims and Hindus -- were killed.

The train fire is controversial because separate inquiries reached different conclusions about how it started.

A 2005 Supreme Court inquiry found the fire was an accident, started by passengers' cooking stoves.

However, last year a Gujarat State Court convicted 31 Muslims for attacking the train and starting the fire. An inquiry set up by the state government said in 2008 that the burning of the train was a "conspiracy," a BBC report said.

This week the court in Ahmedabad convicted the 32 people for involvement in rioting in Naroda Patiya the day following the train fire in 2002.

Former Hindu nationalist Bharatiya Janata Party state politician Mayaben Kodnani was found guilty of murder and criminal conspiracy. Kodnani -- who after the riots went on to be Gujarat's Minister Women and Child Development -- could face the death penalty.

The conviction is the first time a former minister has been convicted in a Gujarat riots case, a report by New Delhi TV said.

"It's a great verdict, we would have liked many more convicted but let's hope that truth and justice will finally prevail," one of the victims said.

Public prosecutor Akhil Desai said no leniency should be shown to those convicted of the crimes which included rioting, murder, arson and attack on a religious structure.

Desai also said he would be arguing for "imprisonment for life" for the guilty, NDTV reported.

The BJP has held power in Gujarat since 1995. But the party, led by Chief Minister Narendra Modi, has been put on the back foot by the court's ruling against its former minister.

"It has been proved now that BJP's minister and officials were involved in the Gujarat riots. Everything that happened was at the behest of Narendra Modi," said federal Congress Party leader Digvijaya Singh.

Gujarat state elections are due by the end of the year.