UN chief Ban Ki-moon has called on Iran to free all its political prisoners on the sidelines of a Non-Aligned Movement summit. "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 Friday 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.