Islamabad, Pakistan - Internet regulators shut down YouTube and hundreds of other websites in protest at the online contest "Everybody Draw Mohammed Day".
Students and Islamist militants marched in their thousands through the cities of Karachi, Lahore and Islamabad.
Any representation of the Prophet Mohammed is deemed un-Islamic and blasphemous by Muslims.
On Wednesday a Pakistani court ordered internet service providers to block customers from Facebook. The following day, most also lost access to Wikipedia, YouTube and more than 450 websites that referred to the online contest.
However, that did not stop Facebook members elsewhere in the world posting photographs and cartoons.
One showed a photograph of a pig with a speech bubble saying: "Peace be upon me and my armies." Another showed Mohammed with a long beard, holding a bomb in one hand and a decapitated head in the other, wearing a T-shirt bearing the legend: "I love Jihad." Organisers said the page was set up to promote freedom of speech but a government spokesman condemned the images.
"Such malicious and insulting attacks hurt the sentiments of Muslims around the world and cannot be accepted under the garb of freedom of expression," said Abdul Basit during a weekly briefing.
The publication of cartoons of the prophet in Danish newspapers in 2005 sparked deadly protests in Muslim countries.
About 50 people were killed during riots when the images were republished in European papers a year later, five of them in Pakistan.
Hardliners from the banned organisation Jamaat-ud-Dawa – considered a front for the militant group blamed for the 2008 Mumbai attacks – organised five separate rallies in Lahore. They promised bigger demonstrations after Friday prayers today.