A mass rally held to condemn Islamic State [IS] in the wake of its latest killing video turned violent in Ethiopia on Wednesday, as protestors hurled stones and police fired tear gas into the crowd.

Tens of thousands of Ethiopians, including Orthodox religious leaders, gathered in the capital city Addis Ababa to express their horror at the latest brutality shown by IS.

The Islamist group last Saturday released a video showing around 15 Ethiopians being beheaded, and another group of the same size being fatally shot in the head in Libya. A subtitle refers to the victims as "worshippers of the cross belonging to the hostile Ethiopian church".

Country authorities have said that they were likely to have been migrants travelling through Libya in the hope of reaching Europe, and have confirmed that those killed were its citizens.

Speaking at the protest, Ethiopia's prime minister Hailemariam Desalegn described the murders as "Satanic", and urged people not to attempt to cross the Sahara.

"This week's cruel act which was committed against our citizens in Libya not only gives a glimpse into terrorism, but also shows the Satanic acts and objectives of those who committed the act," he said, according to the BBC.

"We should strengthen our resolve against any form of terrorism and extremism."

The rally marked the beginning of three days of mourning in Ethiopia for the victims, only two of whom have so far been named.

Ahaza Kassaye, the mother of one of the victims identified as Eyasu Yikunoamlak, told Reuters she was "heartened" to see so many turn out in solidarity with her son and others who were murdered.

"I am in pain. The innocent son of a poor mother butchered like he was," she said. "But I am heartened to see so many Ethiopians mourn him."

However, the largely peaceful protest became violent when some demonstrators directed their anger at authorities. They hurled stones at police, leading to clashes and tear gas being fired. At least 100 people were arrested.

Some expressed anger that the government had failed to protect its citizens, while others claimed that authorities suppress free speech.

Abune Mathias, the patriarch of the Ethiopian Orthodox Tewahedo Church, today blessed relatives of the victims during a prayer ceremony at the Holy Trinity Cathedral in Addis Ababa. He has branded the murders "repugnant", and said the international community has a "duty to raise our voice to tell the world that the killing of the innocent like animals is completely unacceptable".