JAKARTA--Financier Nat Rothschild is considering a bid for the coal assets of London-listed Bumi PLC (VLLRF, BUMI.LN) to counter last month's more than $1.2 billion offer by Indonesia's powerful Bakrie Group, and people familiar with the plans said Friday that one of the family's most high-profile rivals has been approached to join.

The rival, presidential front-runner and general-turned-businessman Prabowo Subianto, had been approached since September and has consistently rejected the approaches, people within the Bakrie camp with knowledge of the matter said. Mr. Subianto's team was campaigning at a local by-election in the east of Indonesia's main island, Java, and didn't immediately answer telephone calls.

The Bakrie Group's patriarch, Aburizal Bakrie, heads Indonesia's Golkar Party and is also a contender in the 2014 presidential elections.

It was unclear whether Mr. Rothschild had found any other takers.

A spokesman for Mr. Rothschild declined to comment on whether Mr. Rothschild was forming a consortium to bid on Indonesian coal assets, but he confirmed that "Nat Rothschild is in talks with a number of parties to see whether a solution is feasible" in which Bumi remains a U.K.-listed company with Indonesian coal assets and with robust U.K.-style corporate governance arrangements.

The spokesman wasn't able to comment on the subject of those talks or the people involved in the talks but said, "An important part of this solution would be a consensual exit for the Bakries, Samin Tan and their associates."

Samin Tan is the chairman of Bumi PLC and owns a coking-coal company, PT Borneo Lumbung Energi & Metal (PBTLY, BORN.JK).

Borneo hopes to get additional compensation from Bakrie Group in a separate deal to unwind Borneo's joint ventures with the Bakrie family. Bumi PLC's share price rose nearly 17% on Friday, while shares of PT Borneo Lumbung Energi & Metal, one of the largest shareholders, closed up 17%. Shares in PT Bumi Resources (BUMI.JK), one of Bumi PLC's Indonesian mining holdings, rose 1.7%.

Bumi PLC said it had taken note of its share price move following media reports on a possible proposal from Mr. Rothschild, but it confirmed that it hasn't received any such proposal.

Bumi PLC was formed last year when the Bakrie Group mines were folded into Mr. Rothschild's investment vehicle. The two sides have been squabbling since over how the assets were managed and as the share price has fallen more than 70% from its listing price.

The boardroom battle escalated amid allegations of email hacking, under investigation by Indonesian police, and the Bakrie Group last month said it wanted to take its assets back and leave Bumi PLC as a cash shell. Mr. Rothschild reacted by resigning from the company's board.

Now it looks as if Mr. Rothschild may be arranging a counterbid, possibly offering more money for some of the assets and trying to bring in a powerful Indonesian partner, said a person familiar with the offer. Under Bakrie Group's current proposal, the conglomerate offered to give up its 23.8% stake in Bumi PLC in exchange for a 10% stake in PT Bumi Resources.

In the second stage of the offer, Bakrie Group would buy Bumi PLC's remaining 18.9% stake in Jakarta-listed Bumi Resources for $278 million. Next, Bakrie Group would buy Bumi PLC's other mining asset, an 85% stake in PT Berau Coal Energy (BCUYF, BRAU.JK), for about $950 million.

Analysts were unconvinced that Mr. Subianto, though a rival of the Bakries, would join a business challenge against them over an area as fraught as Bumi PLC has become.

Jeremy Paul, fund manager for Succorinvest Central Gani, dismissed the idea that Mr. Subianto would be part of a consortium against the Bakries. "I don't buy the story," he said.

Mr. Paul said that any plan from Mr. Rothschild to form a consortium would be more aimed at blocking Bakrie from buying Berau Coal.

--Eric Bellman, Alex MacDonald and I Made Sentana contributed to this article.

Write to Patrick McDowell at Patrick.Mcdowell@wsj.com and write to Edhi Pranasidhu at Edhi.Pranasidhi@dowjones.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires