Silicon Valley venture capital powerhouse Kleiner Perkins Caufield & Byers today announced a new $250 million initiative — sFund — to invest in startups inventing social web applications and services. Amazon.com, Facebook, and Zynga, the company behind hit social games FarmVille and Mafia Wars, have committed to invest in the fund. Other investors are Comcast, Liberty Media, and Allen & Company.

The sFund will "provide financing, counsel, and relationship capital for a new generation of entrepreneurs to deliver on the promise of the social web," Kleiner Perkins said. Amazon's interest appears to be in providing cloud-computing services to social startups.

"Social apps are viral, and when they hit, it often happens suddenly, and then they grow explosively. That's one of the reasons the scalable, elastic, no capex, variable cost nature of Amazon Web Services is ideal for social apps," said Amazon CEO Jeff Bezos, in a statement. "The top three companies that develop for Facebook all use AWS."

Here's what startups get through the fund:

Amazon Web Services (AWS) will provide AWS Getting-Started Support for one year, priority access to worldwide Startup Events, and dedicated business and technical support. Facebook will contribute access to its platform teams, beta APIs, and new programs, like Facebook Credits. Zynga will host periodic sessions with sFund companies to focus on management and technical development, including open source collaboration. Comcast Interactive Capital, Comcast’s venture fund, will provide access to Comcast’s resources, teams, and relationships.

Amazon's cloud has quietly played a behind-the-scenes role with many popular social games, and Amazon clearly sees this as a growth opportunity.

The sFund was announced at Facebook headquarters in Palo Alto with Kleiner Perkins partner (and ex-Amazon director) John Doerr, Amazon CEO Jeff Bezos, Facebook CEO Mark Zuckerberg, Zynga CEO Mark Pincus, and Bing Gordon, a board member of both Amazon and Zynga. Gordon is leading the sFund effort.

More from All Things D's Kara Swisher's live blog of the event.

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