LONDON -- U.K.-listed Bumi PLC (BUMI.LN) said Tuesday that an external investigation was unable to substantiate allegations of financial and other irregularities at its Indonesian coal assets, after key parties were unwilling to be interviewed and because of unanswered questions about the source of some circumstantial evidence.

Bumi said it could not publish the full conclusions of the independent investigation, led by U.K.-law firm Macfarlanes, due to the substantial risk that some materials contained in the final report could violate Indonesian laws if they were made public.

Bumi said the investigation was unable to confirm the source of materials that were handed over by its co-founder and major shareholder, Nathaniel Rothschild, to Macfarlanes. The probe wasn't able to identify the alleged whistleblower who provided the documentation to Mr. Rothschild, Bumi said.

Bumi said that its Chairman, Samin Tan, fully cooperated with the investigation and that the company remains engaged in discussions with the U.K. and Indonesian authorities about the recourses open to it.

The company added that its board intends to proceed with the first part of the Bakrie family proposal which seeks to sever ties between Bumi and the family, by buying back Bumi's 29% stake in PT Bumi Resources Tbk (BUMI.JK) for $278 million in cash plus the cancellation of the family's 24% stake in Bumi, which is held through Bakrie Group.

-Write to Alex MacDonald at alex.macdonald@dowjones.com

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