Ban's appeal for the release of "opposition leaders, human rights defenders, journalists and social activists," made in a speech to an Iranian diplomatic college on Thursday, went without any immediate official response from Tehran.
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Ban stressed 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 is to be chosen.
"Restricting freedom of expression and suppressing social activism will only set back development and plant the seeds of instability," Ban warned.
Ban in Iran, with President Ahmadinejad (Photo: AFP)
The 2009 presidential election in Iran, which saw Ahmadinejad declared the winner amid allegations of fraud, triggered widespread protests that were brutally crushed by the authorities.
The leaders of the opposition movement – Mir Hossein Mousavi and Mehdi Karroubi – have languished under house arrest ever since.
Israel, US responsible for Syria conflict
Also on Friday, the UN chief met with Syrian Prime Minister Wael al-Halaqi and Foreign Minister Walid Muallem, and told them that the fighting must stop in Syria "with the primary responsibility resting on the government to halt its use of heavy weapons."
Ban said in the meeting that he set out "my demands for all sides to cease all forms of violence," with Damascus bearing the greatest responsibility.
Ban added that he had asked Iran to support his call on Syria, "and I have a strong assurance from Iran that it will do so."
Earlier on Friday, Halaqi met Iran's supreme leader Ayatollah Ali Khamenei, who said the United States and Israel were responsible for the Syrian conflict, asserting they were "flooding weapons" to rebels there.
"The main and behind-the-scenes operators behind the painful issues in Syria are America and the Zionist regime," Khamenei said, according to his official website.
Khamenei called the bloodshed in Syria "unacceptable," but said it was "the Syrian government that has been the victim of current events."
He urged Halaqi to "remove all pretexts" preventing the opposition from engaging in dialogue and to press on with promised political reforms.
Halaqi thanked Khamenei for Iran's support, and delivered greetings from Assad, who did not attend the NAM summit.
"The Syrian government is determined to confront all terrorist groups and to cleanse areas of these groups while moving ahead with political reforms and national dialogue," Halaqi was quoted as saying.
Dudi Cohen contributed to the report
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