Nigeria has arrested the chairman of a local oil firm, a security official said yesterday, as part of a widening corruption investigation in Africa's biggest petroleum producer that has also netted former oil minister Diezani Alison-Madueke.

Days after British police detained Alison-Madueke, one of Africa’s most powerful women, the official said Nigeria's Economic and Financial Crimes Commission (EFCC) had arrestedAtlantic Energy chairman Olajide Omokore on corruption and money laundering charges.

The arrests, which follow pledges by President Muhammadu Buhari to “clean up” Africa's biggest economy, have sent shockwaves through Nigeria’s globe-trotting corporate and political elite.

“A lot of people have been shocked,” one oil executive in Nigeria told Reuters. “The net is widening and it’s not clear how deep the rabbit hole goes. There will be a few people looking over their shoulders.”

In response to a Reuters query, Switzerland’s office of the attorney general said it had received a request from Nigeria for “mutual assistance” in connection with Nigerian tycoon Kolawole Aluko and energy firms linked to him.

The EFCC official said that Omokore, listed by Forbes magazine in 2012 as one of “Ten Nigerian multi-millionaires you have never heard of”, remained in custody.

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