Microsoft has inked a search distribution deal with social networking site Facebook.

Satya Nadella, senior vice president in charge of Microsoft's search, MSN and ad platform engineering efforts, said Microsoft "will be providing an API to Facebook where they will create a rich search experience, inclusive of Web search."

It will launch in the fall, and will include both Live Search results and Microsoft search advertising.

The company is positioning it as another effort to broaden awareness of its Live Search engine, which Nadella demonstrated at Microsoft's Financial Analyst Meeting today.

Last August, Microsoft and Facebook inked a display advertising deal. In October, Microsoft bought a 1.6 percent stake in Facebook for $240 million.

Update, 11:15 a.m.: The deal is U.S. only. It is apparently exclusive, as Microsoft will be providing search on Facebook's site, a Microsoft spokeswoman said. I've asked Facebook for confirmation that Microsoft will be, in fact, its exclusive U.S. search provider. Facebook has more than 90 million active users globally.

Upate, 11:23 a.m.: Facebook spokesman Matt Hicks said in an email: "We're not disclosing the terms of the search deal, but it is specifically for the U.S."

If it were exclusive, why wouldn't Microsoft and Facebook come out and say so definitively?

Update, 12:04 p.m.: Just got an update from Microsoft: The deal is exclusive to Microsoft for search in the U.S.