Defeated presidential candidate Mirhossein Mousavi urged supporters to stage protests or gather in mosques to mourn those killed after disputed elections that set off Iran's worst unrest since the 1979 Revolution. President Mahmoud Ahmadinejad's victory against the reformist Mousavi sparked demonstrations and bloody street battles in Tehran which killed at least seven people on Monday while other protests flared up in cities across Iran. “A number of our countrymen were wounded or martyred,” Mousavi said in a statement on his website posted on Wednesday. “I ask the people to express their solidarity with the families ... by coming together in mosques or taking part in peaceful demonstrations,” said Mousavi, adding that he would also take part in the day of mourning planned for Thursday. The bloodshed, mass protests over four days, arrests and a media crackdown focused world attention on Iran. In a warning, Fars News Agency quoted Interior Minister Sadeq Mahsouli as saying “no permission has been issued for a gathering or rally in Haft-e-Tir Square” on Wednesday. State television has said the “main agents” behind the turmoil have been arrested with guns and explosives. After Monday's deaths, Mousavi had urged followers to call off a planned rally in the same downtown area on Tuesday so the marchers headed north instead. Some sent messages to meet again on Wednesday for a rally at Tehran's central Haft-e -Tir Square. Security forces arrested a pro-reform activist and an editor on Wednesday while a provincial prosecutor warned that those causing unrest faced the death penalty. An official inquiry was launched into an attack on university students. Mohammadreza Habibi, prosecutor-general in the province of Isfahan, said: “We warn the few ... controlled by foreigners who try to disrupt domestic security by inciting individuals to destroy and to commit arson that the Islamic penal code for such individuals waging war against God is execution.” A reformist source said Saeed Laylaz, editor of business daily Sarmayeh, and activist Mohammadreza Jalaiepour were both arrested on Wednesday morning. Jalaiepour was detained at Tehran's international airport, the source said. Iran's Interior Ministry ordered a probe into an attack on university students. The political earthquake set off by Friday's vote prompted President Barack Obama, who had urged the Iranian leadership to “unclench its fist”. Obama told CNBC there appeared to be little difference in policy between Ahmadinejad and Mousavi. “Either way we are going to be dealing with an Iranian regime that has historically been hostile to the US,” he said. Ahmadinejad indicated on Sunday that there would be no change in nuclear policy during his second term, saying the issue “belongs in the past”. Mohamed ElBaradei, director general of the IAEA, said on Wednesday Iran wanted the ability to build nuclear weapons to gain a reputation as a major power in the Middle East.