June 20 (Bloomberg) -- Iran’s Security Council warned former Prime Minister Mir Hossein Mousavi against holding further rallies a day after Supreme Leader Ayatollah Ali Khamenei warned that the largest street demonstrations in 30 years must end.

“Your national duty is to avoid encouraging or supporting such illegal gatherings,” council head Abbas Mohtaj wrote in a letter published by the ILNA news agency. “You are certainly bearing in mind that should you encourage such illegal gatherings or activities you will be held accountable for the consequences.”

The letter was in reply to a statement from Mousavi dated June 17 addressed to the council, which backed peaceful demonstrations and accused the police of damaging property.

“We believe this is an organized network that is probably led by groups with ties to foreigners,” the council said. “They are disturbing the public’s peace, order and security and acting against citizens rights.”

Some Iranians plan to go ahead with a rally today, Agence France-Presse reported, citing an aide to defeated candidate Mehdi Karrubi.

The rally, planned for 4 p.m. local time, will take place in Tehran’s Enghelab Square and is being organized by supporters of Karrubi and a group calling itself the Combatant Clerics Assembly, the news agency said.

Rally Violence

Amnesty International reported on its Web site yesterday that at least 10 people have died in violence following the election in which Ahmadinejad sought a second term. The largest of the rallies, on June 15, was the biggest anti-government protest in Iran since the ruling shah was overthrown by the Islamic revolution in 1979.

The protests began after election officials said Ahmadinejad won about 63 percent of the vote, to about 34 percent for Mousavi.

To contact the reporters on this story: Ladane Nasseri in Tehran at lnasseri@bloomberg.net; Ali Sheikholeslami in London at alis2@bloomberg.net.

Last Updated: June 20, 2009 04:18 EDT