The Chilean securities regulator, Superintendencia de Valores y Seguros (SVS), is investigating insider trading in shares of two retail groups, Distribucion y Servicio (D&S) and SACI Falabella, before their announcement in May that they planned to merge.

SVS superintendent Guillermo Larrain suspects inside trading in the companies' shares at least a month before the annoucement, Dow Jones reported.

"We are in the process of formulating the charges, in a rather long and detailed document; as soon as it's ready, we'll send it out," Larrain was quoted as saying. However, Larrain declined to say how many people would be charged or if any of them were executives or on the boards of either retailer.

The merger plans between Falabella, a department store operator, and supermarket group D&S were announced on 17 May. When cleared by anti-trust regulators, the merger would create South America's largest retail group.