Iran’s Supreme Leader Ayatollah Ali Khamenei is to lead Friday prayers in the capital Tehran – the first time he has done so in eight years.
It comes in the wake of widespread angry protests over the Ukrainian passenger plane shot down by Iran’s military last week.
Iran’s leadership is also under pressure over a sharp downturn in the economy brought on by US sanctions.
On Wednesday, President Hassan Rouhani appealed for national unity.
But in a rare sign of friction within the Iranian regime, he also called on the military to give a full account of how it shot down the plane.
The Ukraine International Airlines Boeing 737-800 was travelling to Kyiv from Tehran on 8 January when it crashed shortly after take-off. All 176 passengers on board, including dozens of Iranians and Canadians, were killed.
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The Iranian authorities initially denied responsibility but, after international pressure mounted, the hardline Revolutionary Guards admitted that the plane had been mistaken for a “cruise missile” during heightened tensions with the US.
Hours before it was shot down, Iranian missiles had targeted two airbases in Iraq that housed US forces.
That rocket attack came in response to a US drone strike in Baghdad that killed senior Iranian general Qasem Soleimani.
On Friday, the US said 11 of its troops were treated for concussion after the attack. It initially said none of its troops had been injured.
What’s happening in Iran?
Iran’s Mehr news agency said Ayatollah Khamenei, 80, would lead this week’s Friday Muslim prayers in Tehran’s Mosalla mosque, but it did not link the event to the current situation.
It quoted officials as saying “the Iranian nation will once again demonstrate their unity and magnificence”.
The last time Ayatollah Khamenei led Friday prayers in Tehran was in 2012 on the 33rd anniversary of the country’s Islamic Revolution.
Leading Friday prayers in the capital is a symbolically significant act usually reserved for times when Iran’s highest authority wishes to deliver an important message, says Mehdi Khalaji of The Washington Institute for Near East Policy.
Historically, Iranian leaders have left this task to loyal clerics with strong oratorical skills, he adds.