Pakistan pulled the plug again on YouTube just hours after unblocking the video file-sharing site following a months-long blackout.
Pakistani authorities say that "powerful firewall software" would be used to block inappropriate content on YouTube if and when the service resumes.
The order for the new crackdown came directly from Prime Minister Raja Pervez Ashraf.
Ashraf in September had ordered YouTube blocked after it refused to remove a controversial anti-Islam video.
Weeks of protests in Pakistan over the crudely made film "Innocence of Muslims" resulted in more than 20 people being killed.
Earlier on Saturday the Pakistan Telecommunication Authority (PTA) notified all Internet companies to "immediately unblock/restore" YouTube until further orders were given.
But hours later Ashraf, after officials had said measures were being taken to filter out blasphemous material and pornography, ordered PTA to cut access.
"The prime minister has issued orders to block YouTube again," a senior official in Ashraf's office told AFP, declining to provide more details or a reason for the decision.
The privately run Geo television network reported that Ashraf issued the orders to block YouTube after it showed a report saying blasphemous content was still accessible.
Interior Minister Rehman Malik had said earlier said on Twitter that the decision to allow access again was due to huge public demand.
"PTA is finalising negotiations for acquiring a powerful firewall software to totally block pornographic and blasphemous material," he added.
The Internet Service Providers Association of Pakistan (Ispak) had welcomed the announcement of a restoration.
Ispak Convener Wahajus Siraj told AFP that when the ban first came into force, internet video traffic in Pakistan plummeted by up to 30%.
He said unblocking access would be a positive step because many students and institutions "were using YouTube for education, and were facing difficulties as alternate websites were not as good".
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