In a statement, the Pakistan Telecommunication Authority (PTA) said that YouTube had been blocked due to "objectionable content." It did not give details about the content.
The PTA directed Internet service providers to block YouTube. By late afternoon, most Internet users were unable to access the site.
The move follows the Lahore High Court's order to block Facebook till May 31 as it acted on a petition filed by the Islamic Lawyers Forum, which had sought a complete ban on the social networking website.
The court directed the Foreign Ministry to raise the issue of the blasphemous caricatures of Prophet Mohammed at international fora. It also asked the Foreign Secretary to register a protest with the concerned countries.
Acting on the court's order, the Information Technology Ministry directed the Pakistan Telecommunication Authority to block Facebook and all "other Internet links displaying sacrilegious caricatures" of Prophet Mohammed.
The ministry also directed PTA to "remain alert and watchful and block all such links displaying the profane caricatures immediately", an official statement said. The ministry asked people to inform it about "objectionable caricatures" at any website.
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