Feb 26 (Reuters) - The U.S. Federal Trade Commission will announce on Monday that it is suing to block grocer Kroger's proposed $24.6 billion deal to buy smaller rival Albertsons, a Semafor reporter said on social media platform X.com, citing an unnamed source familiar with the matter.

The deal, which would create a grocery empire with more than 4,000 stores, has drawn tough scrutiny from lawmakers and consumer groups worried about higher grocery prices, job losses, store closures and diminishing choice for consumers.

The FTC's challenge would come ahead of an agreement to not close the deal between the FTC and the two companies that expires on Feb. 28.

The states of Colorado and Washington have already sued to block the deal, which has raised antitrust concerns over higher prices for consumers, store closures and loss of jobs.

Kroger has said retail giants such as Walmart and Amazon.com would become "even more powerful and unaccountable" if its merger with Albertsons was blocked.

Shares of Kroger fell 1%.

(Reporting by Ismail Shakil)