WASHINGTON — Facebook, rumored for some time to be planning its own email service, may finally be on the verge of doing so in a move that would send a shot across the bow of Google, Yahoo! and Microsoft.

TechCrunch, a leading Silicon Valley technology blog, reported Friday that the social network plans to announce a Web-based email service complete with @facebook.com addresses at an event in San Francisco on Monday.

Agence France-Presse and other media outlets have been invited to Facebook's event but have not been told what it will be about.

Facebook boasts more than 500 million members around the world and offering a personal email service would lay down a powerful challenge to the established email giants -- Microsoft's Hotmail, Yahoo! Mail and Google's Gmail.

Hotmail currently has the most users, 361.7 million as of September, according to online tracking firm comScore, followed by Yahoo! with 273.1 million and Gmail with 193.3 million.

TechCrunch said Facebook's planned Web-based email service is part of a secret project known as "Project Titan" that is "unofficially referred to internally as its 'Gmail killer.'"

"And while it may only be in early stages come its launch Monday, there's a huge amount of potential here," TechCrunch's Jason Kincaid noted.

The report comes amid a recent bout of sparring between Facebook and Google over data sharing and Silicon Valley engineering talent.

Google last week blocked Facebook from importing Gmail contact information over the Palo Alto, California-based social network's refusal to reciprocate and share data about its users.

And The Wall Street Journal reported that Internet search king Google, in a bid to stem defections to rival technology firms such as Facebook, has given all of its 23,000 employees a 10 percent pay hike.

According to the Journal, roughly 10 percent of Facebook's employees are Google veterans.

TechCrunch's Kincaid and others noted the advantages Facebook could bring to an email battle.

"Facebook has the world's most popular photos product, the most popular events product, and soon will have a very popular local deals product as well," Kincaid said.

"It can tweak the design of its webmail client to display content from each of these in a seamless fashion.

"And there's also the social element: Facebook knows who your friends are and how closely you're connected to them; it can probably do a pretty good job figuring out which personal emails you want to read most and prioritize them accordingly," he said.

Gadget blog Gizmodo said the prospect of an email service from Facebook should make Google, Yahoo! and Microsoft "very nervous."

"Facebook Mail could be a killer not only because of its potential instant size, but because of its natural advantage at making mail more useful," Gizmodo blogger Jesus Diaz said.

"Actually, it may become the only 100 percent useful mail service out there, only showing you the email you are actually interested in," Diaz said.

"Since Facebook knows how you interact with all your contacts, they would be able to perfectly separate what is important from what is not."

"Of course, not every Facebook user will jump on its mail bandwagon," Diaz added. "But chances are that a huge percentage of the user base will."