From VOA News:

The Iranian government has delivered a stern warning to the country’s main opposition leader not to encourage his supporters to take the streets in protest of the disputed presidential election.
The country’s Security Council issued a statement to defeated presidential candidate Mir Hussein Mousavi Saturday, saying he will be responsible for “consequences of illegal rallies.”
A senior police commander, Ahmad Reza Radan, also said any protests will be dealt with firmly.
The warnings come a day after Iran’s supreme leader, Ayatollah Ali Khamenei, called for an end to nearly a week of massive street protests by opposition supporters who claim the vote was rigged.
In his first address since the June 12 vote, Ayatollah Khamenei also declared incumbent President Mahmoud Ahmadinejad the definitive winner.
Mass rallies were planned for Saturday as well, but it is not clear if supporters will go ahead with demonstrations.
An aide to defeated presidential candidate Mehdi Karroubi told reporters a demonstration set for Saturday has not been canceled and will be held as planned. But state television said a group of moderate clerics had called off the rally in Tehran because no permission had been granted.
Meanwhile, Iran’s Council of Guardians, a powerful body that supervises the elections, convened a meeting Saturday to discuss defeated candidates’ concerns about the election. The Council invited Mr. Mousavi, Karroubi and Mohsen Rezaei, but state media reported that only Rezaei attended.