People collect drinking water from charity tap amid fears of a new cholera outbreak in Sanaa, Yemen November 5, 2018. Picture taken November 5, 2018. REUTERS/Khaled Abdullah

GENEVA (Reuters) - The United Nations appealed for $21.9 billion on Tuesday to address 21 humanitarian crises worldwide next year, including $4 billion for Yemen, its largest aid operation.

The appeal to donor countries does not include the funding requirements for Syria, which are expected to bring the total up to $25 billion, it said.