“The website has been banned by the Ministry of Information Technology and the decision was conveyed to us,” said Mohammad Younis Khan, spokesman for Pakistan Telecommunication Authority (PTA).
“Both Facebook and Twitter were involved. We negotiated with both. Facebook has agreed to remove the stuff but Twitter is not responding to us.”
Twitter had been blocked but Facebook was still available, he said, adding that those responsible for the competition were “trying to hurt Muslim feelings”.
Responding to the furore around the ban, one Twitter user, @vinodvyas, wrote: “Now billions of ppl know there exists a competition to draw Prophet.”
Twitter is widely used in Pakistan, including by prominent public figures such as celebrities, cricketers, cabinet ministers and members of parliament.
Former president Pervez Musharraf, in exile in Britain, regularly tweets, as does Interior Minister Rehman Malik, and Ali Zafar, the popular actor and musician. Asma Jahangir, the leading lawyer, is also on Twitter.
Islam strictly prohibits the depiction of any prophet as blasphemous.
Muslims across the globe staged angry protests over the publication of satirical cartoons of Mohammed in European newspapers four years ago.
A suicide attack outside the Danish embassy in Islamabad that year killed eight people.