The UN health agency has warned about increasing needs in Yemen, as conflict continues to escalate.
In an update, the WHO insisted that $31 million is required urgently, a significant scale-up from the $9 million requested initially.
An additional $700,000 is required for the refugee response in Djibouti, where some 3,800 people have fled so far.
According to the Yemeni authorities, clashes between Houthi opposition fighters and Saudi forces have led to 959 reported deaths and more than 4,200 injuries in 10 governorates.
Almost 200,000 people have been displaced since the escalation began and many have been uprooted more than once.
The UN agency noted that less than one per cent of all those displaced in Yemen have gone without access to health services, meaning that many households in Taiz and Lahj have gone without adequate assistance.
