TEHRAN (Reuters) - Supporters of Iran’s defeated presidential candidate Mirhossein Mousavi prepared to heed his rallying call for a national day of mourning on Thursday for those killed in post-election clashes.

(Editors’ note: Reuters and other foreign media are subject to Iranian restrictions on their ability to report, film or take pictures in Tehran.)

State media said seven people were killed in an opposition protest in Tehran against what Mousavi says was a rigged election last week in favor of hardline incumbent President Mahmoud Ahmadinejad.

On his website, Mousavi called on Iranians to stage peaceful demonstrations or gather in mosques on Thursday.

“In the course of the past days and as a consequence of illegal and violent encounters with (people protesting) against the outcome of the presidential election, a number of our countrymen were wounded or martyred,” he said.

“I ask the people to express their solidarity with the families ... by coming together in mosques or taking part in peaceful demonstrations.”

Official results from Friday’s vote showed Ahmadinejad had won a landslide, leading to daily clashes between Mousavi backers, anti-riot police and Islamic militiamen. Authorities have dismissed opposition allegations of vote rigging.

Despite calls by Supreme Leader Ayatollah Ali Khamenei for national unity, Mousavi supporters have continued to pour on to the streets.

Bloodshed, mass protests, arrests and a media crackdown have focused attention on the world’s fifth-biggest oil exporter which is locked in a dispute with the West over its nuclear program.

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On Wednesday, tens of thousands demonstrated in central Tehran for a fifth day against Ahmadinejad’s official victory, which has caused the worst unrest since the 1979 Islamic revolution.

“INTERVENTIONIST” PROTESTS

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Reformist clerics have requested permission from the governor of Tehran to hold a rally in the city on Saturday, to be attended by Mousavi and reformist former President Mohammad Khatami, Mousavi’s website said.

Iran’s Foreign Ministry on Wednesday summoned the Swiss ambassador, who represents U.S. interests, to protest at “interventionist” U.S. statements on the country’s election.

In Washington, the State Department strongly rejected the criticism and the White House said President Barack Obama would continue to defend the right of Iranians to protest peacefully against the outcome of the election.

Mousavi sent a letter to Iran’s state national security council complaining of plainclothes agents using sticks, metal rods and sometimes firearms to “attack the lines of peaceful participants before the arrival of the security forces.”

He condemned arrests of his allies in the past few days. Dozens of pro-reformers have been detained since Friday’s election, including senior figures, sources say.

The ISNA news agency, quoting provincial officials, said 88 people had been arrested during post-election unrest in the conservative northeastern city of Mashhad and up to 60 people in Tabriz in the northwest.

Pro-Mousavi protests were also reported in the cities of Isfahan, Rasht, Orumiyeh, Zanjan and Zahedan.