The U.K.’s Competition and Markets Authority said Friday that is consulting on the launch of an investigation into Apple Inc.’s AAPL, -3.60% and Alphabet Inc.’s GOOGL, -2.01% Google’s market power in mobile browsers and Apple’s restrictions on cloud gaming through its App Store.

The regulator is also taking action against Google over its app store payment practices.

A report by the CMA found that Apple and Google have an effective duopoly on mobile ecosystems that enables them to exercise a stranglehold over the markets, which include operating systems, app stores and web browsers on mobile devices.

Without intervention, the companies are likely to strengthen their positions in the sector, further restricting competition, it said.

Write to Kyle Morris at kyle.morris@dowjones.com