A UN humanitarian official has appealed for more than four billion dollars (£3.1 billion) in life-saving aid for more than 10 million Syrians, saying that the country’s largely forgotten crisis remains “one of the most deadly to civilians in the world”.

Adam Abdelmoula, resident coordinator in Syria for the UN Office for the Coordination of Humanitarian Affairs, made the appeal days after Syria marked the 13th anniversary of the civil war that has killed nearly a half million people and left large parts of the country destroyed.

Mr Abdelmoula told reporters in Geneva: “Today, we are facing an unprecedented situation in Syria – one that we cannot afford to ignore.

“Inaction will be costly for all of us and will inevitably lead to additional suffering.”

About 16.7 million people require some form of humanitarian assistance in Syria, an increase from 15.3 million last year, he said.

More than seven million people are internally displaced and nearly as many are refugees in other countries, including neighbouring Jordan, Lebanon and Turkey.

The war has left 90% of Syria’s population below the poverty line as millions face cuts in food aid because of a funding shortfall. The UN World Food Programme ended its main assistance scheme in the country in January.

“The Syria crisis remains one of the most deadly to civilians in the world. Hostilities continue to plague various parts of Syria and have recently seen a sharp spike, especially in the north,” Mr Abdelmoula said.

He suggested that Israel’s war against Hamas in Gaza had given cover for more military activity in parts of Syria.

“We saw the world’s attention focusing on Gaza, and that provided some kind of diversion of attention that allowed the significant escalation of hostilities in the north-east without much attention being paid to that situation by the international community,” Mr Abdelmoula added.