A number of properties in Switzerland have been raided in connection with suspected money laundering involving Angola's $5bn sovereign wealth fund and central bank, news agency Reuters reports.

The Swiss prosecutors' office announced it conducted the raids on Friday "as part of the criminal proceedings being conducted against persons unknown on suspicion of money laundering".

The country's attorney general opened the investigation in April, months after it was revealed Angola's sovereign wealth fund had paid tens of millions in fees to a Swiss-Angolan businessman Jean-Claude Bastos de Morais, who works closely with José Filomeno dos Santos, the former president's son.

They deny any wrongdoing.

There were no further details on the raids.