(Reuters) -Activision Blizzard said on Wednesday it has extended the deadline for the close of its $69 billion takeover by Microsoft to Oct. 18 as the companies work to secure approval from the United Kingdom's antitrust authority.

The "Call of Duty" publisher said the companies also agreed to increase the deal termination fee to $3.5 billion from $3 billion if it does not close by Aug. 29. The fee will further rise to $4.5 billion after Sept. 15.

The two U.S. companies originally agreed to close the deal by July 18, but U.S. regulatory efforts to block the takeover and Britain's push to restructure it have delayed the close.

The U.S. Federal Trade Commission's (FTC) bid to temporarily stop the deal was denied twice, first by a federal judge and then by an appeals court.

Britain's Competition and Markets Authority (CMA) had earlier decided to block the deal, but reversed course last week and extended its deadline for a final ruling to Aug. 29 after the U.S. court ruling left Britain alone in opposition.

Regulators in both countries have varying concerns over the deal.

The FTC said the deal could let Microsoft degrade Activision's game quality or player experience on rival consoles like Nintendo and Sony Group Corp's PlayStation, as well as manipulate pricing or change terms or timing of access to Activision content.

The CMA questioned whether the deal could hinder competition in the cloud gaming industry, where users can play on any device using subscriptions such as the Xbox Game Pass that offer a wide selection of games.

Microsoft responded to these concerns by offering 10-year licensing deals to rivals after the deal closes. The latest was an agreement with Sony Group to keep "Call of Duty" on PlayStation, the biggest competitor to Microsoft's Xbox.

(Reporting by Chavi Mehta and Yuvraj Malik in Bengaluru; Editing by Devika Syamnath)