The move came hours after Interior Minister Rehman Malik's claim in a message posted on Twitter early this morning that no restrictions would be imposed on the popular micro-blogging site. The Information Technology Ministry said Twitter had been blocked for publicising "blasphemous and inflammatory content".
Calls for participation in the contest for blasphemous caricatures were being made on Twitter, it said. The ministry said Twitter was blocked after it failed to respond to several requests from Pakistan for taking action against blasphemous content.
The ministry claimed it had contacted Twitter several times but the site's administrators had failed to respond. Users from across Pakistan reported that they were unable to access the site on their computers and mobile phones since the afternoon.
An estimated six million people use Twitter in Pakistan. Earlier, Malik himself tweeted that the government had no plans to impose restrictions on Twitter and Facebook. "Dear all, I assure (you) that Twitter and (Facebook) will continue in our country and it will not be blocked. (Please) do not believe in rumours," he posted in a tweet.
In another tweet, Malik dismissed a question from a New York Times reporter about reports that the government intended to restrict access to Twitter. "Why (should) I even think of doing so?" Malik asked.
The Pakistan Telecommunication Authority blocked access to Twitter directly without notifying Internet Service Providers, said Wahaj-us-Siraj, convener for the Internet Services Providers Association of Pakistan.