Adds background throughout, updates shares

June 1 (Reuters) - Media mogul Barry Diller's company People Inc IAC.O is preparing an offer to buy MGM Resorts MGM.N, valuing the casino giant at more than $18 billion, the New York Times' DealBook reported on Monday.

MGM's shares rose more than 10% in premarket trading, while those of People - renamed from IAC in April - rose nearly 3%.

The report comes just weeks after Diller, the digital media company's chairman, told shareholders in an April 28 letter that People would sharpen its focus on its MGM stake, calling the stock "wildly undervalued."

People is planning to bid $48.30 a share in cash for the 73.9% stake in MGM Resorts that it does not already own, the report said.

MGM Resorts and People did not immediately respond to Reuters requests for comment.

Diller's interest in MGM dates back to the COVID-19 pandemic, when he began accumulating shares in the casino operator when its shares were battered by closures and travel restrictions.

MGM owns marquee properties that account for roughly 40% of the Las Vegas Strip. However, the casino operator has been struggling with sluggish footfalls in Las Vegas, and in recent quarters has relied on growth in its China properties, including Macau, and digital operations.

People's offer could mark another major takeover attempt in the casino sector. Last week, hospitality billionaire Tilman Fertitta's firm announced the takeover of Caesars Entertainment CZR.O in a $17.6 billion deal.