July 6 (Reuters) - Britain's antitrust watchdog said on Wednesday it had started an investigation into Microsoft Corp's $68.7 billion deal to buy "Call of Duty" maker Activision Blizzard Inc.

The Competition and Markets Authority (CMA) said it had until Sept. 1 to make its phase 1 decision on whether the deal between the U.S. technology company and video-game maker Activision would reduce competition in the United Kingdom.

"We're committed to answering questions from regulators and ultimately believe a thorough review will help the deal close with broad confidence, and that it will be positive for competition," Lisa Tanzi, corporate vice president and general counsel of Microsoft told Reuters in an emailed statement.

"We expect and think it's appropriate for regulators to take a close look at this acquisition," Tanzi said.

Activision did not immediately respond to requests for comment.

In the biggest gaming industry deal in history, Microsoft said in January it was buying Activision Blizzard. According to Refinitiv data, the Microsoft-Activision deal would be the largest all-cash acquisition on record.

The CMA's phase 1 investigation will either lead to the deal being cleared or will move to a more in-depth phase 2 review. (Reporting by Sinchita Mitra and Amna Karimi in Bengaluru; Editing by Vinay Dwivedi and David Clarke)