LONDON — British regulators say that the corporate battle between 21st Century Fox and Comcast to take over broadcaster Sky will be settled by auction.

The Takeover Panel, an independent regulator, says that since neither company has declared its offer final, an auction procedure is expected to commence at 5 p.m. on Sept. 21 and end during the evening of Sept. 22.

Comcast has put down a £26 billion ($34.3 billion) offer for Sky. Fox has bid £24.5 billion for the 61 percent of the satellite broadcaster it does not own.

The panel will make an announcement setting out the prices of the offers at the end of the auction.

Auctions of this sort are very rare.

Sky operates in Austria, Germany, Ireland and Italy as well as the U.K. It has 22.5 million customers, attracted by offerings such as English Premier League soccer and "Game of Thrones."

Fox, which is run by media mogul Rupert Murdoch, still faces significant regulatory battles in Britain. The challenges include the culture secretary's assertion that Fox would have to sell Sky News to win government approval because of concerns about media plurality.

Fox's bid for Sky is the most recent episode in Murdoch's long-running effort to take full control of the company.

His last bid foundered amid a 2011 phone-hacking scandal, in which journalists working for Murdoch newspapers were accused of gaining illegal access to the voicemail messages of crime victims, celebrities and members of the royal family. News Corp., which is controlled by the Murdochs, withdrew its bid for Sky soon after.

Both Comcast and Fox want Sky in order to amass more programming as they compete for viewers with both traditional TV networks and technology companies such as Netflix and Amazon.