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Shares in Petrofac have dived almost 30% after the oilfield services firm suspended its chief operating officer Marwan Chedid amid a fraud inquiry.

The Serious Fraud Office is probing the firm over allegations of "bribery, corruption and money laundering" relating to oil contractor Unaoil.

Petrofac said Mr Chedid had been arrested by the SFO earlier this month and later released without charge.

But he has now been suspended "until further notice" and has quit the board.

Chief executive Ayman Asfari, who was also arrested and released without charge, will continue in his role, although he will not be involved in any matters connected to the investigation, Petrofac said.

Chairman Rijnhard van Tets said: "These decisions signal the board's determination to co-operate fully with the SFO and its investigation, whilst ensuring Petrofac continues to deliver for its clients."

Wider investigation

Earlier in May the SFO confirmed it was investigating Petrofac as part of a wider investigation into Unaoil, a Monaco-based firm that it has accused of corruptly securing contracts for dozens of multinationals.

It followed an internal investigation by Petrofac whose findings have been rejected by the SFO.

On Thursday, Petrofac said it had formed a special board committee to manage the firm's dealings with investigators. It is made up of its chairman, chief financial officer and independent non-executive directors.

Citing the "scale of the investigation", it has also called in an external specialist to oversee the firm's response to the probe.

Petrofac says it engaged Unaoil for the provision of local consultancy services, primarily in Kazakhstan, between 2002 and 2009.

It previously claimed to have found no evidence of wrongdoing with regards to its ties to the firm.

Unaoil has denied claims it helped British and other companies win contracts by bribing politicians and government officials.