Facebook is expected to launch a new messaging system seen as a challenge to Google's Gmail, Yahoo and Hotmail. The giant social network - which boasts more than 500 million users worldwide - will host a special event in San Francisco on Monday. Unconfirmed reports suggest Facebook could announce its own e-mail address - @facebook.com - or even a fully-fledged web-based e-mail system. Google-Facebook rivalry has increased recently amid a series of disputes. Google has banned Facebook from importing its users' e-mail contacts, a move it says it made because Facebook refused to allow the export of contact and friend data from within user profiles. In reply, Facebook enabled a workaround that let users save their Google contacts to their computers before importing them into Facebook. 'Treasure trove' According to a report on popular technology blog Techcrunch, Facebook's new venture - codenamed Project Titan - is being dubbed a "Gmail killer". The blog suggests Facebook is preparing to unveil a fully-fledged e-mail service for the web. It also suggests that Facebook's wealth of information on users - from event planning, to their likes and even the frequency with which they interact with other users - could be used to make the e-mail service an irresistible proposition. But little is known for sure, and it is also possible that the new system could be a revamped messaging service only available for Facebook users. Facebook has made no comment on the report, and will brief the press in San Francisco on Monday at 1000 (1800 GMT). Facebook's huge user base is seen as a potential treasure trove of information, especially for advertisers. Analysts say the social networking firm, founded by Mark Zuckerberg, is becoming an increasingly powerful rival to Google because of the loyalty of its user base. Facebook users willingly provide reams of private and personal information, as well as interacting constantly with friends, applications and organisations through the Facebook platform. Jesus Diaz of technology blog Gizmodo said that while Google had the most to be concerned about, other e-mail providers would also be worried. "If I were Google, Yahoo or Hotmail, I'd be very nervous," he told the BBC. "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." While it has struck a deal with Microsoft to allow user data to power its Bing search engine, it has made no such arrangement with rival Google. Google insists it believes in open-sharing of information, and stopped Facebook mining Gmail for contact information because Facebook itself was keeping contact information private. The companies have also become bitter rivals offline as well as online, with Facebook's reportedly offering Google engineers lucrative deals to defect across Silicon Valley. Last week, Google awarded staff a 10% pay rise and will pay employees more of their total package through salaries instead of bonuses. Analysts said this move was partly influenced by a desire to hold onto staff being wooed by Facebook. Source: BBC