About 200 Assyrians and other Christians gathered in a church east of Beirut in solidarity with the victims in Syria and Iraq.

Islamic State militants seized more Christians from their homes in northeastern Syria in the past three days, bringing the total number abducted by the extremist group to over 220, activists said on Thursday.

At the same time, the extremists also released a video showing the continued destruction of the heritage of the lands under their control. It depicted men using sledgehammers to smash ancient Mesopotamian statues and other artefacts in Iraq’s northern city of Mosul.

The video, coinciding with mounting fears over the fate of the captive Christian Assyrians in Syria, sent a fresh wave of dread across the region, particularly among minorities who feel targeted by the group.

“Daesh is wiping Assyrian heritage in Mosul, and at the same time wiping them geographically from the face of the Earth,” said Osama Edward, director of the Assyrian Network for Human Rights in Syria. He referred to the Islamic State by its Arabic acronym.

About 200 Assyrians and other Christians gathered in a church east of Beirut in solidarity with the victims in Syria and Iraq. Some cried openly.

One man held a banner that read: “We will not surrender, we will not be broken.” A few young men said they were preparing to go to Syria to fight and help their brethren defend their homes against the Islamic State group.

The destruction of artefacts in the Mosul museum is part of a campaign by IS extremists who have destroyed a number of shrines including Muslim holy sites to eliminate what they view as heresy. They also are believed to have sold ancient artefacts on the black market in order to finance their bloody campaign in the region.

In the video released on Thursday, militants used sledgehammers and drills to smash and destroy several large statues, which are then shown chipped and in pieces. The five-minute video also shows a black-clad man at an archaeological site in Mosul, drilling through and destroying a winged-bull an Assyrian protective deity that dates to the 7th century B.C.

The video was posted on social media accounts affiliated with the Islamic State group. Although it could not be independently verified by The Associated Press, it appeared to be authentic, based on knowledge of the Mosul Museum.

A professor at the Archaeology College in Mosul confirmed to the AP that the two sites depicted in the video are the city museum and a location known as Nirgal Gate, one of several gates to the capital of the Assyrian Empire, Ninevah.

“I’m totally shocked,” Amir al-Jumaili said by phone from outside of Mosul, Iraq’s second-largest city. “It’s a catastrophe. With the destruction of these artefacts, we can no longer be proud of Mosul’s civilisation.”

Very few of the museum pieces are not genuine, he said.

Irina Bokova, director-general of the U.N.’s culture agency UNESCO, said in a statement that she was “deeply shocked” at the video. She said she asked for an emergency meeting of the U.N. Security Council be convened “on the protection of Iraq’s cultural heritage as an integral element for the country’s security.”

“I condemn this as a deliberate attack against Iraq’s millennial history and culture, and as an inflammatory incitement to violence and hatred,” Ms. Bokova said.

Mosul and surrounding Nineveh Province fell to the militants in June 2014 after Iraqi security forces melted away.

In their push, the extremists captured large parts of both Iraq and neighbouring Syria. They declared a self-styled caliphate on territories that are under their control, killing members of religious minorities, driving others from their homes, enslaving women and destroying houses of worship.

The Iraqi region under the control of the extremists has nearly 1,800 of the country’s 12,000 registered archaeological sites, and the militants appear to be out to cleanse it of ideas they consider un-Islamic, including library books, relics and even Islamic sites considered idolatrous.

“The so-called Assyrians and Akkadians and others looked to gods for war, agriculture and rain to whom they offered sacrifices,” said a man in the video, referring to groups that that left their mark on Mesopotamia for more than 5,000 years in what is now Iraq, eastern Syria and southern Turkey.

Islamic State militants ransacked the Central Library of Mosul in January, smashing the locks and taking about 2,000 books, while leaving only Islamic texts. Days later, militants broke into University of Mosul’s library and built a bonfire out of hundreds of books on science and culture, destroying them in front of students.

“Is this how Assyrians who gave civilisation are rewarded,” asked Mr. Edward from his base in Stockholm. “What is all this hate?”

Among the most important sites under the militants’ control are four ancient cities — Ninevah, Kalhu, Dur Sharrukin and Ashur, which at different times were capitals of the mighty Assyrian Empire. The Assyrians first arose around 2,500 B.C. and once ruled from the Mediterranean coast to what is now Iran.

In Syria, fears mounted over the fate of the abducted Christians, with at least 220 now being held captive, according to activists.

An Assyrian in Beirut whose parents and sister were among a dozen relatives abducted said he called his father’s mobile phone Monday and got a man who said: “This is the Islamic State.” The man then briefly put the Assyrian’s father on the line, and he said in a terrified voice not to worry, that they were being treated well. His relatives’ mobiles have since been shut off. The Beirut resident spoke on condition of anonymity because he feared for his relatives’ lives.

The abductions began on Monday, when militants attacked a cluster of villages along the Khabur River, sending thousands of people fleeing to safer areas. The Britain-based Syrian Observatory for Human Rights said the militants picked up dozens more Assyrians from 11 communities near the town of Tal Tamr in the next few days.

The Province, which borders Turkey and Iraq, has become the latest battleground in the fight against the Islamic State group in Syria. It is predominantly Kurdish but also has populations of Arabs and predominantly Christian Assyrians and Armenians.

Younan Talia, a senior official with the Assyrian Democratic Organisation, said IS had raided 33 Assyrian villages, seizing as many as 300 people. Mr. Edward said his group had documented the names of 255 missing people.

It was not possible to reconcile the numbers, and the fate of the hostages remained unclear.

“We are praying for them and we are fasting,” said the Assyrian in Beirut. “I don’t care if they burn the villages down, but please let them return safe.”