The lack of funds has caused deep cuts in assistance, the organisation said on Tuesday.
In September, the WFP said 2.2 million people in the southern African country faced food shortages, the highest in four years, following a drought and poor harvest.
The WFP had hoped to increase the number of people under its relief operations to 1.8 million but said it was instead being forced to reduce the number of recipients due to a lack of cash.
"In fact, we've had to cut rations for one million of our beneficiaries in recent months and there are likely to be deeper cuts as from next month," it said in a statement.
The monthly ration is made up of cooking oil, beans and maize, the staple food.
The WFP said it needed 60 million US dollars to implement full relief operations in the next six months in the impoverished nation of 13 million.
The 2.2 million in need of food aid is the highest since early 2009, the end of a decade-long economic decline.