The Pakistan Telecommunication Authority told the country's 70 Internet service providers Friday that the popular Web site would be blocked until further notice.
The authority did not specify what the offensive material was, but a PTA official said the ban concerned a movie trailer for an upcoming film by Dutch lawmaker Geert Wilders, who has said he plans to release an anti-Quran movie portraying the religion as fascist and prone to inciting violence against women and homosexuals.
The PTA official, who asked not to be identified because he was not an official spokesman, said the Pakistan Telecommunication Authority also blocks Web sites that show controversial drawings of the Prophet Muhammad. The drawings were originally printed in European newspapers in 2006 and were reprinted by some papers last week.
The PTA urged Web users to write to YouTube and request the removal of the objectionable movies, saying authorities would stop blocking the site once that happened.
Pakistan is not the only country to have blocked access to YouTube.
In January, a court in Turkey blocked the site because some video clips allegedly insulted the country's founding father, Mustafa Kemal Ataturk. It is illegal to insult Ataturk in Turkey.
Last spring the Thai government banned the site for about four months because of clips seen as offensive to Thailand's revered monarch, King Bhumibol Adulyadej.
Moroccans last year were unable to access YouTube after users posted videos critical of Morocco's treatment of the people of Western Sahara, a territory Morocco took control of in 1975.