The third anniversary of the start of the Syrian conflict will fall on Saturday, a tragic milestone in what has become the greatest humanitarian disaster of th e 21st century.

Since violence erupted in the country on March 15, 2011, more than 100,000 people have been killed, 10,000 of them children. Almost nine million Syrians need humanitarian aid.

Many have fled the violence, taking refuge in neighbouring countries. Others have been forced from their homes by the fighting but remain trapped in Syria without safe access to food, clean water or shelter.

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Every day, the conflict grows more deadly and the trauma for those trying to survive increases. A report released today by Save the Children highlights the horrifying effect the war has had on its youngest victims.

A Devastating Toll: The Impact Of Three Years Of War On The Health Of Syria's Children shows the health crisis caused by the conflict is claiming even more lives than the bombs and bullets.

Millions of children are at risk from the collapse of the country's health system. Doctors and nurses are forced to engage in brutal medical practices and a series of epidemics have left children exposed to deadly diseases.

Just three years ago, the country had a fully functioning medical set-up and children attended school every day. But three years of bloodshed and violence have cut short thousands of young lives and destroyed childhood for many more.

The report reveals terrible stories of this crisis: newborn babies dying in their incubators because of power cuts; children with burns or fractures having limbs amputated because clinics don't have the equipment needed to treat them; and patients opting to be knocked unconscious with metal bars because there is no anaesthetic. It is horrific and it is preventable.

Vaccination programmes have stopped, causing a resurgence of deadly diseases including polio, measles and meningitis. These can maim, paralyse and even kill, and were almost unheard of before the conflict. As many as 80,000 Syrian children are thought to be infected with polio's most aggressive form and are silently spreading the disease. Sadly, once children get sick, they are increasingly unlikely to receive effective treatment.

Save the Children's report found that hospitals have been targeted, patients have been attacked in their beds and doctors on duty have been killed or imprisoned. Across Syria, more than 60% of hospitals are no longer functional and almost half of the country's doctors have fled altogether. Just 36 remain in Aleppo, a city of more than two million people, where there should be at least 2500 doctors.

The impact is devastating but unsurprising: 200,000 Syrians have died of treatable chronic diseases such as cancer, asthma and diabetes, double the number killed by the ongoing violence. Many thousands will have been children. Everyday conditions are becoming fatal because of a lack of m edication or access medical care, .

Last month, the UN Security Council secured a resolution on humanitarian access for impartial agencies such as Save the Children. This is vitally important for the millions of people stuck in Syria with no access to medicines, vaccines or clean water.

But it is just a first step. The international community is failing Syria's children and world leaders must stand up for the young victims of this conflict and send a clear message that suffering and death will no longer be tolerated.

Access should be widened to aid across conflict lines and inside siege areas. This could mean the difference between life and death for millions of children and their families.

On Thursday, public events will take place in more than 30 countries as people around the world shine a spotlight on the crisis.

I'll be leading a candlelit vigil with Save the Children supporters at sunset in Edinburgh to show that, while we continue to hope for a peaceful end to the conflict, we won't falter in our efforts to help the most vulnerable victims of this war.