The heads of major UN organisations on Monday called for access to civilians cut off from humanitarian aid in Syria, saying the world “must not stand silent” even though the high-profile siege of the Syrian city of Aleppo is over.

The joint appeal came from Davos in Switzerland, as business, political and cultural elites gather there for the World Economic Forum. The UN’s refugee agency (UNHCR), the humanitarian aid coordinator Ocha, the children’s agency Unicef, the World Food Programme (WFP) and the World Health Organisation (WHO) all called for “immediate, unconditional and safe access” to all Syrian families and children in need.

According to the statement, up to 700,000 people – nearly half of them children – live in 15 besieged areas of Syria.

Many lack “the most basic elements to sustain their lives” and face “continued risk of violence”, said the statement.

WFP’s director, Ertharin Cousin, Anthony Lake of Unicef, Stephen O’Brien of Ocha, Margaret Chan of the WHO and Filippo Grandi of UNHCR were striving to keep international attention focused on the nearly six-year civil war in Syria, which was estimated in 2016 to have left nearly half a million people dead.

Last month, Russian air power helped forces supporting Syria’s president, Bashar al-Assad, to crush the opposition-held enclave in the northern city of Aleppo, a major win for Assad’s forces, which had besieged the rebels for months.

“The horrors of the siege of the eastern districts of Aleppo have disappeared from the public consciousness – but we must not let the needs, the lives and the futures of Syria’s people fade from the world’s conscience,” the UN agency chiefs said in the statement.

“We must not let 2017 repeat the tragedies of 2016 for Syria,” they said.