The United Nations says more than three million people have fled Syria's civil war, creating what it calls "the biggest humanitarian emergency of our era."

In a statement Friday, the U.N. refugee agency said one million of those refugees fled in the past year alone from the "increasingly horrifying conditions" in Syria.

The statement said the figure does not include hundreds of thousands who have not registered as refugees. It also said a further 6.5 million are displaced within Syria.

The U.N. estimates that half of Syria's population has now been forced to abandon their homes since the fighting began in March 2011. Almost half of those are children.

Most of the refugees have fled to Lebanon, Turkey or Jordan, where the U.N. says they arrive in a "shocking state, exhausted, scared and with their savings depleted."

The U.N. high commissioner for refugees, Antonio Guterres, said the world is "failing to meet the needs of refugees and the countries hosting them."

The world body says it needs another $2 billion by the end of this year to help those affected by the conflict.

David Miliband, the head of the International Rescue Committee, said the new refugee count represents "three million indictments of government brutality, opposition violence and international failure."

The former British foreign secretary said the "appalling milestone needs to generate action as well as anger" and called for "greatly increased efforts" to reduce the suffering of those affected by the conflict.