At least 10 Iranians were killed and more than 100 injured in clashes with police during protests in the capital Tehran on Sunday against elections results.
State media is calling those who died "terrorists", as Tehran remains in a high state of tension amid a continuing crackdown on protesters.
But opposition leader Mirhossein Mousavi has urged supporters to continue their protests over the disputed presidential election. In a statement posted on his website, Mr Mousavi says it is the right of Iranians to protest against lies and frauds.
About 23 journalists have been arrested while trying to cover the protests, while heavy restrictions on foreign journalists have limited them to reporting from their offices as the government attempts to block websites and social-networking sites.
American magazine Newsweek says a Canadian journalist, who has worked for it for a decade, has been detained without charge and has not been seen or heard from. And BBC correspondent John Leyne has been expelled from the country.
The United States which has grown more vocal in its support of the protesters, has been watching the social network sites Twitter, YouTube and Facebook closely.
Iran has accused Britain and the US of meddling in its affairs, and has hammered home its message by ordering the BBC correspondent's expulsion.
Leyne has been told to leave Iran just two days after Ayatollah Ali Khamenei accused Britain of adopting an "evil" position in the face of a week of deadly protests.
British Foreign Secretary David Miliband has dismissed the comments, saying his country has played no part in supporting the violent street protests.
Iran's foreign minister says officials are looking into complaints about the country's disputed presidential election and will announce the results of their investigation by the end of the week.
Iran's top legislative body, the Guardian Council, is examining complaints by the defeated candidates, including Mr Mousavi, that the election was rigged.
State TV says "terrorists" were killed during clashes with police, and that "rioters" set alight two petrol stations and a mosque and attacked a military post.
Iran's head of police has warned that any further unrest over the election results will be "decisively confronted".
Riot police fired teargas and used batons and water cannon to disperse protesters in Tehran on Saturday.
Witnesses said there were between 2,000 and 3,000 protesters, much fewer than the hundreds of thousands earlier in the week.
The BBC reports that police used live ammunition, and that one man was shot and others injured amid running fights.
The rally was in defiance of a warning from Supreme Leader Ayatollah Ali Khamenei that protests should stop. In a speech on Friday Ayatollah Khamenei endorsed disputed election results that gave Mr Ahmadinejad a victory.
A suicide bomber killed himself at the mausoleum of the father of Iran's Islamic revolution, Ayatollah Ruhollah Khomeini.
Three other people were wounded in the attack, according to the English language station Press TV. It was not clear who carried out the bombing.
Mr Mousavi made it clear on Saturday he would not back down.
In a public address in southwestern Tehran, Mr Mousavi said he was "ready for martyrdom" in leading protests and called for a national strike if he is arrested, a witness said.
In a statement reported by the semi-official Fars news agency, Mr Mousavi said he was not confronting the state, but added that if authorities did not allow legal rallies, Iran might face "dangerous consequences".
US President Barack Obama has called on Iran's government to "stop all violent and unjust actions against its own people".
"The Iranian government must understand that the world is watching. We mourn each and every innocent life that is lost," Mr Obama said.
On Friday, Iran's highest legislative body said it was ready to recount a random 10% of the votes cast in the 12 June poll to meet the complaints of Mr Mousavi and two other candidates who lost to Mr Ahmadinejad.