Nigeria's finance minister says Africa's richest economy is borrowing money to pay salaries as it struggles through a "difficult cash crunch" brought on by halved oil prices.

Minister Ngozi Okonjo-Iweala tried to be upbeat in a speech after the legislature Tuesday approved a 2015 budget thrice revised because of slashed oil prices. Oil provides 80 percent of revenues for the government of Africa's biggest petroleum producer.

She said "revenue challenges" have prohibited the release of any funds for capital expenditure though food prices and single-digit inflation remain quite stable.

It's bad news for the incoming government of President-elect Muhammadu Buhari, who takes over May 29 from incumbent Goodluck Jonathan.

Okonjo-Iweala said the government already has borrowed more than half of the budgetary borrowing provision to pay salaries and other overheads.