Iraqi Christians gathered in Baghdad this weekend to mark Easter but celebrations were tempered by fears Islamic State would eradicate their shrinking community, even as the army launched a U.S.-backed offensive to retake Mosul, their ancestral homeland.

In mid-2014, Christians in Mosul were forced to flee when Islamic State seized the northern city and began destroying centuries-old religious sites, ending a presence that once numbered in the tens of thousands and dates back to Christianity’s earliest years.

U.S.-backed Iraqi forces launched an offensive against Islamic State last week touted as the beginning of a broader campaign to clear areas around Mosul, though progress has been slow.

“We are threatened with extinction. This is a harsh word but every day we are being depleted. Our people are traveling, migrating,” said Father Muyessir al-Mukhalisi, a priest at Saint George’s Chaldean Church in east Baghdad.

Like millions of other Iraqis forced to leave home by the jihadist group’s seizure of a third of the country, members of the Christian minority have moved from northern towns and villages to the capital or other cities, and many have joined the masses fleeing to Europe.