Soldiers have staged a coup in Gabon, an OPEC member state, on the fourth day after disputed presidential elections, Bloomberg reports.

It was the ninth in sub-Saharan Africa in the last three years, following a coup in Niger last month. Military coups are caused by economic difficulties and weak governance, which fuel civilian discontent and the spread of extremist violence, especially in West Africa.

On Wednesday, early in the morning, army officers appeared on Gabonese state television to announce the cancellation of elections scheduled for Saturday and the dissolution of the country's institutions. President Ali Bongo is under house arrest along with his family and a doctor, and his son has been detained.