BEIRUT (Reuters) – Children have suffered the most in Syria’s six-year war, and among them the most vulnerable are those separated from their families, a senior Unicef official told Reuters on Wednesday.

Furthemore, as well as the large number of direct casualties from warfare, many more children have died or suffered from indirect consequences of the crisis including a collapse in healthcare.

“For unaccompanied and separated children the situation is even harsher than for other children, and for children in general it’s already a very, very difficult situation,” said Geert Cappelaere, Unicef regional director for the Middle East and North Africa.

Unicef, the United Nation’s agency focusing on children, issued a report on Monday on the war in Syria, which began after protests six years ago against President Bashar al-Assad.

In its report, Unicef said it had documented the deaths of 652 children last year, 20 percent more than in 2015. But Cappelaere said that represented only a small proportion of the real number of deaths.

“In 2016 every six hours a child dying or severely injured in Syria … dramatic figures. But these are only the figures we have been able to verify. We do assume that indeed the number of child casualties is really much higher,” he said.

Documenting the real impact of the war is “an impossible task,” he added.

Cappelaere returned on Tuesday from a three-day visit to Damascus, Homs and Aleppo, a city that suffered massive destruction in siege-and-bombardment fighting that culminated late last year when the army overran a last rebel-held pocket.

He was speaking to Reuters in an interview in Beirut, the capital of Lebanon, where more than a million Syrians have sought refuge from the war, including many who now live in informal, makeshift camps with few services.

Cappelaere said that in the Jibreen shelter for displaced people in Aleppo on Tuesday, each of the three newly arrived families he spoke to was carrying a child separated from its family – a measure of the extent of the problem.

“Many of these children are also undocumented. They don’t have their paper…. The problem is not only for tracing (their families), but also for registering in the shelter, the problem of registering them in the schools,” he said.

Even more than other children in Syria’s war, those separated from their families are vulnerable to exploitation.

Already about three-quarters of children in Syria are working and there is what Cappelaere called a “very rapid” rise in the number of early marriages, particularly among girls, because families cannot afford to feed and look after them.

However, there are still signs of hope amid the devastation, Cappelaere said.

“We were driving out of Aleppo yesterday – 15 minutes of driving in the midst of rubble – and suddenly we see two, three, four children with their backpacks on the way to school,” he said.

(Reporting by Angus McDowall; Editing by Hugh Lawson)