(Reuters) -Elon Musk's xAI has nearly doubled gas turbines at its Tennessee data center, exceeding previously known figures and surpassing the number for which the company has submitted permits, according to a letter from community groups to the county's health department.

The Southern Environmental Law Center and local groups have called on the health department to cease operating all the turbines till the company complies with the critical Clean Air Act and local protections.

Reuters could not independently verify the allegations, and the Environmental Protection Agency, Shelby County Health Department and xAI did not immediately respond to requests for comment.

"The dozens of turbines operating outside the datacenter likely make xAI the largest industrial source of the smog-forming pollutant NOx in Memphis," Southern Environmental Law Center said in a statement.

The data center's expanded turbine operations and resulting emissions require xAI to obtain a "major source permit", yet the company operates the equipment without any regulatory authorization, the group added.

The massive surge in power consumption of AI-supporting data centers in the United States is driving an increase in the usage of fossil fuels as clean-energy deployments struggle to keep up.

Billionaire Musk had dubbed the Tennessee data center, which powers the firm's Grok chatbot, as "the most powerful AI training cluster in the world" last year.

The environmental law group said xAI's 35 gas turbines have a capacity of 422 MW, comparable to the Tennessee Valley Authority's Brownsville gas power plant, which has a capacity of 425 MW.

It had said in August that xAI's Memphis data center had installed nearly 20 gas turbines with a combined capacity of about 100 MW.

The Greater Memphis Chamber said in December that xAI planned to expand its Memphis supercomputer to house at least one million graphics processing units.

In late March, the AI firm acquired Musk-owned X in a deal that values the social media platform at $33 billion.

(Reporting by Akash Sriram in Bengaluru; Editing by Devika Syamnath)