A record 12.3 million Syrian children are in need of aid both inside the country and in the wider region where they fled, the United Nations warned.

This comes more than a decade since a civil war devastated Syria yet funding has been “dwindling” over time, the UN said on Sunday.

“Syria’s children have suffered for far too long and should not suffer any longer,” UNICEF, the UN children’s agency, said in a statement.

The agency noted more than 6.5 million children inside Syria are in need of assistance, the highest number recorded since the beginning of the crisis more than 11 years ago.

Syria’s war is estimated to have killed half a million people and displaced millions since it began with a brutal crackdown on anti-government protests in 2011. It escalated to pull in foreign powers and a variety of armed groups.

“Children’s needs, both inside Syria and in neighbouring countries, are growing,” said Adele Khodr, UNICEF’s Middle East chief.

“Many families struggle to make ends meet. Prices of basic supplies including food are skyrocketing, partially as a result of the crisis in Ukraine.”

Among the most vulnerable, children are bearing the brunt of the war’s effect, the UN said.

“In Syria’s neighbouring countries, strained by political instability and fragility, nearly 5.8 million children depend on assistance – their lives riddled with poverty and hardship,” Khodr added.

UNICEF said it faced a severe cash shortfall to provide aid.

“Funding for humanitarian operations is fast dwindling,” Khodr said. “UNICEF has received less than half of its funding requirements for this year.”

UNICEF called for $20m to fund “cross-border operations” in northwest Syria – the country’s last major rebel enclave – to create “the only lifeline for nearly one million children”.