Women and children are most often the fatal victims of air bombardments and other explosive weapons in the four-year Syrian war that has killed roughly 80,000 civilians, according to study results released Tuesday.

Researchers at the Center for Research on the Epidemiology of Disasters at Université Catholique de Louvain in Belgium say that while men make up the overall majority of civilians killed in the war, nearly 25 percent of all civilians killed by explosive weapons were women and children.

Children are most likely to be killed by shells and ground-level explosives in Syria — more so than men, according to the study, which was published Tuesday in the British Medical Journal.

“Our analysis indicates that using explosive weapons in populated areas in Syria has disproportionately lethal effects on women and children and should be urgently prohibited,” the authors wrote. “If we are looking for root causes of the migrant and refugee crises in Europe today, this is surely a major contributor.”

The researchers, led by epidemiologist Debarati Guha-Sapir, wanted to know how many Syrian civilians have been killed by the war, as well as their demographics and how they were killed.

Knowing whether women and children have been targeted, or how civilians have died, can clarify whether human rights have been violated. But such a protracted conflict as the Syrian war makes it difficult to track fatalities, and epidemiologists say that detailed breakdowns of the weapons used to kill people during war aren’t often studied.

In Syria, rumors of chemical weapons use have dogged the government of President Bashar al-Assad as it battles insurgent groups, and deadly barrel bombs dropped by the Syrian army on opposition-held regions have driven civilians into neighboring countries in recent months.

So the researchers honed in on data gathered by the Center for Documentation of Violations in Syria (VDC), one of four groups whose tally of fatalities helped form a comprehensive 2014 U.N. report that said more than 191,000 people had been killed in Syria between March 2011 and April 2014. (PDF)

But the U.N. report, the authors noted, included both fighters and civilians among the fatalities. The VDC, a network of activists who track deaths in Syria, is the only group that has been able to distinguish whether a person killed is a civilian or a combatant, the study said. The VDC recorded some 78,769 violent deaths of civilians in Syria between March 2011 and January 2015.

While studying the victims by gender, age and weapons used, the researchers found that nearly 25 percent of all civilians killed in the conflict were women and children. The data show children are those most likely to be killed by air bombardments, shells and ground-level explosives, more so than adult men or women. Children made up 16 percent of civilians killed in opposition-controlled areas and 23 percent of those killed in government-controlled sectors, the study said.

In most cases, children were killed by shelling and air bombardments, which accounted for 75 percent of the nearly 9,400 deaths of children, the study said.

“The government and rebel factions in Syria typically claim that the targets of their bombs and shells are enemy combatant strongholds, but our findings indicate that for Syrian children these are the weapons most likely to cause death,” the authors wrote, adding that children killed in Iraq were also most likely to have been killed by bombs or shells.

Child deaths caused by ground-level explosives such as car bombs were five times as likely in government-controlled areas as they were for adult men. Women were the second most likely to be killed by explosive weapons, behind children. Women were most often the victims of chemical weapons, followed by air bombardments and shelling.

“The examples of suicide bombing of children at schools (by unknown perpetrators) and of barrel bombs being dropped by helicopters repeatedly over hospitals by government forces indicate that indiscriminate weapons can be used in a targeted manner against children and other civilian groups,” the study’s authors said.