Pakistan on Sunday blocked access to Twitter in response to "blasphemous" material posted by users on the microblogging and social networking website, a senior government official said.

"This has been done under the directions of the Ministry of Information Technology. It's because of blasphemous content," said Mohammed Yaseen, chairman of the Pakistan Telecommunication Authority (PTA).

"They (the ministry) have been discussing with them (Twitter) for some time now, requesting them to remove some particular content," he said.

Pakistan blocked access to Facebook, Twitter, YouTube and about 1,000 other websites for nearly two weeks in May 2010 over blasphemous content.

Any representation of the Prophet Mohammad is deemed un-Islamic and blasphemous by many Muslims, who constitute the overwhelming majority in Pakistan.

PTA chairman Yaseen did not specify which users or messages had prompted the ban. The Internet Service Providers Association of Pakistan said its members have been asked to block Twitter indefinitely, but no reason has been provided by the government.

Yaseen said the ban would be lifted after ongoing discussions between the Pakistan government and Twitter about the allegedly blasphemous material are resolved.

Officials from the Ministry of Information Technology and from Twitter were not immediately available for comment.

Twitter has become increasingly popular in Pakistan in recent years, its users including politicians and government officials.