Increasing numbers of Syrian children are being abducted and forced into combat, according to Unicef's regional director for the Middle East.

"Children increasingly are being killed on the battlefield as combatants," Dr Peter Salama said, according to the Guardian. "This is one of the most insidious trends in Syria".

Although children over 16 have been involved in the military in the past, their involvement has previously been restricted to non-combat roles, Salama added.

"We are seeing a very different pattern today.

"The majority of those children are now under the age of 15, which is a very different pattern to previously. The majority are forced to join, often abducted. They are being used as uninformed, armed checkpoints, and sometimes as forced labour."

Several hundred children have been conscripted and around four hundred have been killed, some of them in combat, he said, adding that these numbers "represent the tip of the iceberg."

Unicef has identified more than 4,000 assaults on schools since the beginning of the Syrian civil war in 2011, 47 of which took place last year.

According to Salama, "We are seeing children killed and maimed in schools and playgrounds by all parties".

Before the civil war, more than 90 per cent of Syrian children attended school, but "nearly a fifth of children going to school [now] have to cross a front line to get to school to do their exams," he said.

"We now have 2.8 million children out of school in Syria and surrounding countries. For many children, they have never been in school in the past five years and so for many primary school children, they have never seen inside a school room."

"The despair felt by a generation of children who see their hopes and futures shattered" is having a destructive impact on the country, Salama warned.

"Urgent concerted efforts and resources are needed to save this generation of children – and it can start at next week's conference in London. It's a race against time," he said, referring to an upcoming conference on the Syrian humanitarian crisis to be held in early February.

The UN agency has launched a campaign to raise £806 million to fund humanitarian aid in Syria and the surrounding areas.