Iran announced on Tuesday its first arrests over the shooting down of a Ukrainian airliner last week, as it struggles to contain the fallout from the disaster that sparked three days of protests.

The Ukraine International Airlines plane was brought down by a missile shortly after takeoff on Wednesday, killing all 176 passengers and crew on board.

Iran has come under mounting international pressure to ensure its investigation into the tragedy is full and transparent.

The authorities’ handling of the air disaster has also angered some Iranians. Videos posted online Monday purported to show hundreds of protesters taking to the streets for a third consecutive night, apparently shouting slogans against the Islamic republic.

Protesters chanted “Death to dictator” on Sunday, Fars news agency reported, a rare move for a country where media usually refer to demonstrators as “rioters” and refrain from publishing such slogans.

The protests have been much smaller than nationwide demonstrations against fuel price hikes that turned deadly in November.

Tehran for days denied Western claims based on US intelligence that the Boeing 737 had been downed by a missile.

It came clean on Saturday when Revolutionary Guards aerospace commander Brigadier General Amirali Hajizadeh acknowledged a missile operator had mistaken the plane for a cruise missile and opened fire independently.

At a televised news conference, the judiciary announced the first arrests had been made over the calamitous blunder, without specifying how many.

“Extensive investigations have been carried out and some people have been arrested,” said spokesman Gholamhossein Esmaili. The announcement came shortly after President Hassan Rouhani said everyone responsible for the disaster must be punished. “For our people it is very important in this incident that anyone who was at fault or negligent at any level” face justice, Rouhani said.

“Anyone who should be punished must be punished.

“The judiciary must form a special court with a high-ranking judge and dozens of experts... The whole world will be watching,” Rouhani said.

“It cannot be that only the person who pressed the button is at fault. There are others, and I want this to be explained to the people explicitly.”

The Kiev-bound plane was shot down at a time when Iran’s armed forces were on heightened alert after launching a volley of missiles at Iraqi bases housing US troops.