Bankrupt Texas utility Energy Future Holdings will abandon a deal to sell power transmission company Oncor to Warren Buffett's Berkshire Hathaway for $9 billion and will accept a $9.45 billion bid for Oncor by Sempra Energy instead, people familiar with the matter said.

The development represents a rare blow for Buffett, who avoids bidding wars for companies and had swooped in two months ago to buy Oncor after two previous attempts by Energy Future to sell it were blocked by Texas regulators.

Energy Future's board decided to make the switch on Sunday after Sempra also offered assurances it could get its acquisition of Oncor approved by Public Utility Commission of Texas (PUCT), as well as a U.S. bankruptcy judge, the sources said.

Berkshire offered to allow Energy Future to keep an Oncor dividend, but that proposal was not enough to bridge the gap in price, the sources added.

The sources asked not to be identified because the decision has not yet been officially announced. Sempra, Oncor and Berkshire did not immediately respond to requests for comment.

Hedge fund Elliott Management, which is Energy Future's biggest creditor, had opposed the sale to Berkshire, arguing it undervalued Oncor and threatening to veto the deal. Elliott had also been trying to put together its own bid for $9.3 billion to buy Oncor.

Elliott has indicated it would support Oncor's sale to Sempra, one of the sources said.

Berkshire had told the PUCT it would accept "ringfencing" on its acquisition of Oncor, restricting its ability to extract cash from the company or add more debt to it. Sempra has now indicated it will also accept some form of ringfencing, according to the sources.

Dallas-based Oncor delivers power to more than 3.4 million homes and businesses through roughly 122,000 miles (196,000 km) of transmission and distribution lines.