Image copyright AP Image caption The oil industry in Nigeria is is widely seen as being plagued by corruption

Nigeria has signed a preliminary $4.5bn (£2.9bn) deal with US-based Vulcan Petroleum to build six oil refineries.

The deal could boost refining capacity in the country by 180,000 barrels a day, with two of the refineries due for completion this year.

Nigeria is Africa's biggest oil producer but its refineries are only able to refine a fraction of this into fuel.

As a result, it is forced to import much of its fuel at great cost.

The memorandum of understanding with Vulcan marked "the beginning of changing our old paradigm of exporting just raw materials and exporting jobs to Western countries," said Nigeria's Trade and Investment Minister Olusegun Aganga.

Last week, Nigerian President Goodluck Jonathan sacked the boss and several other executives of the state oil company, NNPC, after a probe into the industry found $6.8bn had been lost due to fraud in the past two years.

The fuel sector probe was set up in the wake of angry protests in January after the government tried to remove a fuel subsidy.

The government says subsidising fuel cost the country $8bn in 2011.

But the probe found that the government had been paying subsidies on more fuel than the country consumed.