BHP Billiton says it has received approval from US regulatory authorities to proceed with its takeover of shale oil explorer and developer, Petrohawk Energy. BHP Billiton said the Committee on Foreign Investment in the US (CFIUS) now had approved the deal, saying there were no national security implications involved. This followed the Federal Trade Commission's early termination of a waiting period required for the bid under local legislation. "Accordingly, all regulatory approvals conditions to the tender offer have been satisfied," BHP said in a statement. "The documents related to the tender offer have been filed with the US Securities and Exchange Commission."