"Many African countries do not have sufficient funds to finance national control campaigns fully and avoid crop losses," it said on Thursday.
"Aircraft, pesticides, vehicles, sprayers, monitoring capacity and technical support are lacking in all affected countries."
The region is facing its most serious locust crisis in 15 years, with swarms of desert locust moving from northwest Africa into Mauritania, Mali and Niger, where many of the people are subsistence farmers.
FAO said there was also a moderate risk that swarms would reach Darfur, Sudan, where violence has already left two million people short of food and medicine.
Desert locust swarms usually contain about 50 million insects per square kilometre and can travel up to 150km a day. They can devastate entire crop fields in minutes, adult locusts munching their own weight, about two grams, a day.
The swarms are stoking fears of famine, and the Rome-based
UN agency said the situation was deteriorating in countries
like Mauritania and Mali.
"FAO estimated that up to around $100 million are needed to
control the current locust upsurge and stop it from developing
into a full-scale plague," it said in a statement.
It said the international community had already earmarked
$32 million in aid, and FAO said it had provided another $10 million from its own resources. Some African nations have also mobilised their own resources.