Pakistan pulled the plug again on YouTube just hours after unblocking the video file-sharing site following a months-long blackout.
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 reporters, declining to provide more details or a reason for the decision.