Economic growth is expected to rise to 3.4 percent in sub-Saharan Africa next year from 2.6 percent in 2017, the IMF said in a report on Monday, but warned that rising debt and political risks in larger economies would weigh down future growth.

IMF Headquarters, Washington, D.C., United States.

Nigeria and South Africa are the biggest economies in Africa south of the Sahara, but both nations have been clouded by political uncertainty linked to the tenure of their leaders.

The IMF said a good harvest and recovery in oil output in Nigeria would contribute more than half of the growth in the region this year while an uptick in mining and a better harvest in South Africa as well as a rebound in oil production in Angola will add to growth.

But political uncertainty loomed large in Nigeria, where President Muhammadu Buhari is afflicted by illness, causing speculation about whether he is well enough to run Africa’s biggest economy.