The protests were in response to groups and pages like "Everyone Draw Mohammed Day," which criticizes the Muslims who responded negatively to South Park's depictions of the Prophet and suggested that thousands of Facebook users draw images of Muhammad — an act forbidden by Islamic law. The page has just shy of 3,000 fans, and it hosts several visual depictions of the Prophet.
Pakistan blocked Facebook allegedly for the same reasons last week. The bans will be temporary in both countries; it's likely that access will be restored once the offending images are removed — and they will be. Facebook's policy is to allow access to offending content outside of the countries where it's offensive while censoring it in sync with individual countries' laws within their own borders.
Update: We're getting conflicting reports from different news outlets and sources — some say the ban was made in part because of images of the Prophet, others say it was solely because of the political caricatures. Either way, students have been organizing protests to demand renewed access to the social network.