President Hassan Rouhani appealed Wednesday for "unity" and flagged the need for radical changes to the way Iran is run, after a wave of angry protests over the accidental downing of a Ukrainian airliner.

The Kiev-bound Boeing 737 was shot down in a catastrophic error shortly after takeoff from Tehran, killing all 176 people aboard. One week on from the disaster, Rouhani called for "national unity" in remarks broadcast live on state television.

"If there was a delay" by the armed forces to release information about what happened, "let them apologise," he said. Rouhani also sought a full explanation after it took Iran days to admit the airliner had been mistakenly shot down.

The blunder sparked four consecutive nights of protests in Tehran calling for those responsible to resign or be prosecuted, leading to at least 30 arrests. Iranian Foreign Minister Mohammad Javad Zarif said they were demonstrating after being deceived for days.

"In Iran... people can state their views. Sometimes they state their views in excessive ways, sometimes the reaction is excessive," he said in New Delhi. "But the fact of the matter is, (over the) last few nights we've had people in the streets of Tehran, demonstrating against the fact that they were lied to for a couple of days."

Khamenei to lead prayers

Without linking it to the current situation, state news agency IRNA said Iran's supreme leader Ayatollah Ali Khamenei would lead Friday prayers in Tehran this week. It would be the first time he has done so in nearly eight years.

The latest protests have been much smaller than nationwide demonstrations against fuel price hikes in November that Amnesty International said left more than 300 dead in a crackdown by security forces.

The Ukraine International Airlines plane was downed with Iran on high alert hours it fired a volley of missiles at US troops stationed in Iraq.

The attack on Iraqi bases was launched in retaliation for a US drone strike that killed Qasem Soleimani, the top commander of the Iranian Revolutionary Guards' foreign operations arm.

Rouhani also said Iranians wanted "diversity" as he urged the electoral authorities to refrain from disqualifying would-be candidates for a February 21 general election.

That would mark a major shift in a country where all candidates are vetted for their loyalty by constitutional watchdog the Guardian Council.

"The people are our masters and we are its servants," Rouhani said.