The Pakistani government blocked access to YouTube on Thursday because of "sacrilegious" content on the video-sharing Web site, signaling a growing crackdown against Web sites deemed offensive to the country's majority Muslim population.The move against YouTube came a day after the government blocked access to Facebook because of a page on the social networking site that encouraged users to draw and post images of Islam's Prophet Muhammad. The page sparked criticism because Islam prohibits any images of the prophet.Since 2007, Swedish caricaturist Lars Vilks has has faced numerous threats over his sketch of the prophet with a dog's body. Earlier this year, US investigators said he was the target of an alleged murder plot involving Colleen LaRose, an American woman who dubbed herself "Jihad Jane." Vilks's ordeal inspired a satirical South Park episode showing Muhammad as a bear. The episode was censored after sparking protests.The Pakistan Telecommunications Authority did not point to specific material on YouTube that prompted it to block the site, only citing "growing sacrilegious contents." The government took action against both Facebook and YouTube after it failed to persuade the websites to remove the "derogatory material," the regulatory body said in a statement.It welcomed representatives from the two websites to contact the Pakistani government to resolve the dispute in a way that "ensures religious harmony and respect."The regulatory body said it has blocked more than 450 Internet links containing offensive material. It is unclear how many of the links were blocked in the last two days.Access to the online encyclopedia site Wikipedia and the photo sharing site Flickr also was restricted Thursday.