Iran's Mousavi urges peaceful rallies on Thursday

TEHRAN (Reuters) - Defeated presidential candidate Mirhossein Mousavi has called on supporters to stage peaceful demonstrations or gather in mosques on Thursday to express solidarity with people killed in post-election unrest.

State television has said seven people were killed on Monday in a big opposition protest in downtown Tehran against what Mousavi says was a rigged election in favor of hardline incumbent Mahmoud Ahmadinejad.

"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," Mousavi said.

"I ask the people to express their solidarity with the families .... by coming together in mosques or taking part in peaceful demonstrations," he said on his website.

Saturday's announcement of official election results showing Ahmadinejad had won a landslide has led to days of clashes between Mousavi backers, anti-riot police and Ahmadinejad supporters. The authorities have dismissed opposition allegations of vote rigging in Friday's election.

After Monday's deaths, Mousavi urged followers to call off a planned rally in the same downtown area the following day.

Tens of thousands of his supporters marched instead on Tuesday in northern Tehran. On Wednesday, a big crowd of pro-Mousavi demonstrators gathered in a downtown square in a fifth day of protests.

Mousavi, a moderate advocating better ties with the West, said his supporters wanted to protest calmly.

"Therefore those rioters who damaged public property and create tension in the society are not part of us," he said. "People have chosen peaceful methods and they avoid violence."

Mousavi sent a letter to Iran's state national security council complaining about plainclothes men using sticks, metal rods and sometimes firearms to "attack the lines of peaceful participants before the arrival of the security forces."

They incited the demonstrators and destroyed public property and motor vehicles, the letter said according to his website.

"I would like to call the attention of the council to this heinous phenomenon that officials of the security forces are using these plainclothes men," he said.

During the post-election violence, police have accused "bandits" of setting buses to fire, breaking windows of banks and other buildings, and damaging public property.

On his website, Mousavi 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 were arrested during post-election unrest in the northeastern city of Mashhad and up to 60 people in Tabriz in the northwest.

(Reporting by Hashem Kalantari and Parisa Hafezi; writing by Fredrik Dahl; editing by Andrew Dobbie)