Its seems like many Facebook users like me across the globe are not able to log in as the server seems to be down 27th March 2015 14:00 UTC.
Facebook Will Be Back Soon
Facebook is down for required maintenance right now, but you should be able to get back on within a few minutes. In the meantime, read more about why you're seeing this message. Thanks for your patience as we improve the site.
While trying to login to my Facebook Account I got the above message, It seems like Facebook servers are down for maintenance purposes and should be back in some time. Facebook seems to be making some improvements to its database in certain regions of the world.
This will not affect your account and you'll be able to log in to Facebook with the same password. The help page adds that they do not carry site maintenance on all accounts at the same time, so it's possible that your friends will be able to access the site while your account is unavailable.
So let's be patient, the site should be back soon!

Update: There seems to be an outrage with hashtag #facebookDown on twitter, though Facebook handle on twitter has not yet twittered anything about it
Update: 28th March 2015: Facebook servers are up and running!...
Hashtags : #FacebookServerDown- Facebook Graph API Unavailable
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