News Corp is not interested in buying popular microblogging site Twitter and will not sell its struggling social network MySpace, said the media conglomerate's chief executive, Rupert Murdoch.

Murdoch, who arrived on Wednesday at the Allen & Co investment bank's Sun Valley media and technology conference, said Twitter would be a tough investment to justify because it has not yet come up with a sustainable way to make money.

"Be careful of investing here," he said of Twitter.

Speculation is running rampant at the 27th Sun Valley conference over which company might want to buy Twitter. The service, which lets people post to Web what they are thinking or doing in 140 characters or less, is growing in popularity.

Twitter co-founder Evan Williams is widely considered one of the darlings of this year's conference. Sun Valley often features hot Internet start-ups that older media conglomerates would like to buy to enhance their own businesses.

Asked if he was considering buying Twitter, Murdoch said, "No." Asked about selling MySpace, he said, "Hell no."

News Corp bought MySpace in 2005 for $580 million when the social networking service was nearing the height of its popularity, particularly among younger Internet users.

Since then, it has ceded ground to rival Facebook as well as Twitter. News Corp recently ousted MySpace co-founder and CEO Chris DeWolfe and installed its own management team.

In a bid to cut costs, MySpace also has laid off more than 400 workers, or 30 percent of its staff, in the United States. It also has laid off more abroad.

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