The US is increasingly reliant on oil from West Africa for its daily energy needs and forecasts that up to 25 per cent of imports will hail from the Gulf of Guinea by 2015.

Ghana, which discovered oil offshore only recently, is set to become a producer next year. Some Ghanaians say Barack Obama’s choice of the country for his first presidential visit to sub-Saharan Africa was partly related to ambitions to ensure an interest in the country’s estimated 3-4bn barrel reserves. The US is still Africa’s foremost trading partner ahead of the European Union and China. But the vast majority of US investment in Africa is in oil and gas, and to a lesser extent mining. Given its growing strategic importance to the US economy, African security has become a growing priority for Washington too, with spending on training and operations rising to nearly $1bn in recent years.