BEIRUT — The number of Christians abducted by the Islamic State group in northeastern Syria has risen to 220 in the past three days, as militants round up more hostages from a chain of villages along a strategic river, activists said Thursday.

In Iraq, the IS extremists released a video purportedly showing militants using sledgehammers to smash ancient artifacts in Iraq’s northern city of Mosul, describing the relics as idols that must be removed.

This week’s abductions of the Christian Assyrians in northeastern Syria is one of the largest hostage-takings by the Islamic State since their blitz last year that captured large swaths of both Syria and Iraq last year. The fate of the captives was not known.

The Britain-based Syrian Observatory for Human Rights said the militants picked up dozens more Christian Assyrians from 11 communities near the town of Tal Tamr in Hassakeh province.