The Islamic State’s takeover of the ancient Syrian city of Palmyra, in addition to endangering a host of priceless ancient Roman artifacts, has heralded in the news of yet another massacre at the hands of the terrorist group, with some estimating up to 400 civilian women and children have been killed for having ties to the regime of Syrian President Bashar al-Assad.

The UK’s Sky News is reporting that 400 civilians, mostly women and children, have been killed, many beheaded, in the city. The number was broadcast, Sky News reports, on Syrian television. In addition to civilians killed, the Daily Mail reported late last week that Islamic State terrorists had killed 300 Syrian army soldiers. It is quite possible that the number of deaths will surpass 1,000 by the time the Islamic State fully cements its control over the city and begins implementing radical Sharia law on remaining residents.

The massacre has overwhelmed the city, with both Sky and the Daily Mail, as well as eyewitnesses speaking to human rights groups, describing the streets of Palmyra as being littered with “hundreds of bodies” of those killed during the takeover. Included in the massacres were not just soldiers, but civilian workers who were paid by the government. Sky News notes in particular that the head of the city hospital’s nursing department and her entire family were slaughtered. The Daily Mail published an especially harrowing photo of one Palmyra street lined with bodies (warning: graphic):

The Syrian Observatory for Human Rights, a watchdog group within the country, estimates that at least 13 children have been killed in the slaughter, though they cannot confirm a number. In addition to those already killed, the group tells CNN that up to 600 people are being kept in captivity by the radical Islamist group.

Multiple reports indicate that ISIS has already begun beheading a number of those prisoners. “IS executed 17 people, including civilians and loyalist fighters. At least four of them were beheaded,” the director of the Syrian Observatory for Human Rights Rami Abdel Rahman told the Agence France-Presse last week. That number is expected to rise as ISIS cements its stranglehold on Palmyra.

In addition to the astounding loss of life, academics and archaeologists have sounded the alarm on the danger presented to the city’s historical heritage. Palmyra is a UNESCO World Heritage Site and boasts a formidable collection of ancient Roman architectural treasures and artifacts. In addition to genocide and mass rape, the Islamic State has dedicated itself to the destruction and black market sale of such artifacts, hammering artifacts in the Museum of Mosul to pieces and bulldozing ancient sites like Nimrud, Iraq, when given the opportunity. It is believed that they will do the same to Palmyra in the name of opposition to “idolatry.”

Al-Azhar, an Egypt-based major Sunni religious body, is calling on Muslims and non-Muslims alike to unite to help preserve Palmyra and eradicate the Islamic State. In a statement released on Sunday, Al-Azhar described “protecting archaeological sites from destruction and plundering” as a “battle of all of humanity” against barbarism. The Al-Azhar group includes both a mosque and a university, and many consider the latter to be “Sunni Islam’s most prestigious.” The institution has previously called for the mass killing and crucifixion of Islamic State terrorists.