The US is entering a legal battle with Xbox-maker Microsoft to block its plan to purchase the gaming firm behind hit titles such as Call of Duty.

Regulators cited competition concerns, saying they feared that if the deal went through, Activision Blizzard's games would stop being offered on non-Microsoft gaming consoles.

The Activision purchase was set to be the biggest in Microsoft history.

The company said it would fight to complete the $69bn (£56bn) deal.

Microsoft president Brad Smith said the company had "complete confidence in our case and welcome the opportunity to present our case in court".

The complaint against Microsoft is among the most-high profile legal fights to emerge from US President Joe Biden's pledge to take a harder line against monopolies.

The planned deal had already raised concerns in other countries, including the UK.

Activision Blizzard owns some of the most popular games in the world, including the Call of Duty series, World of Warcraft, Overwatch, and Candy Crush.

The Federal Trade Commission, the US consumer watchdog that filed the complaint, said that Activision was one of a small number of top video game developers that made high-quality games for multiple devices.

The deal would give Microsoft "both the means and motive to harm competition" by manipulating pricing, making games worse on its competitors' video game consoles, "or withholding content from competitors entirely, resulting in harm to consumers," the agency said in a press release.

The FTC pointed to Microsoft's acquisition of ZeniMax, which owns video game studio Bethesda Softworks. Microsoft has said several of the studio's future games will be exclusive to Microsoft consoles.

Microsoft earlier this week said it had agreed to make Call of Duty available on Nintendo for 10 years if the purchase went through.

"This sounds alarming, so I want to reinforce my confidence that this deal will close," Activision Blizzard chief executive Bobby Kotick wrote in a letter to staff that was shared on the company's website. "The allegation that this deal is anti-competitive doesn't align with the facts, and we believe we'll win this challenge."

BBC News