IS has "destroyed Assyrian monuments in Syria and Iraq. We ask the international community, especially the UN, to hold a Security Council meeting" to decide on military intervention, Hovik Behboud, an organiser, told AFP.
"We are gathered here for the international community to hear our voice and seek their help in the release of prisoners," said Nancy Aldo, one of the demonstrators, who wore orange scarves as a sign of solidarity with the Assyrians kidnapped by IS in northern Syria.
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Last week, the Islamic State (IS) group bulldozed the ancient ruins of Nimrud, a city in northern Iraq founded in the 13th century BC and considered one of the jewels of the country's Assyrian period.
In February, IS militants kidnapped 220 Assyrians in the mainly Kurdish province of Hasakeh and have reportedly released 19 of them for ransoms.
Iran's own Assyrian minority, numbering around 25,000, is officially recognised by the authorities and has one representative in parliament.