There has been some issue with Facebook servers being down or extremely slow today causing it to be unavailable in many regions including Pakistan.
Although there is issue with facebook in Pakistan and other Muslim countries for many months, but probably they don’t care to fix it or something similar, however, this time this issue affected people across the globe.
Facebook official page says:
We’re currently experiencing some site issues causing Facebook to be slow or unavailable for some people. We are working to resolve this issue as quickly as possible.
Hopefully it will be available soon.