Turkey and Thailand have in the past also banned access to the site

Its telecommunications authority ordered internet service providers to block the site until further notice.

Reports said the content included Danish cartoons depicting the Prophet Muhammad that have outraged many.

But one report said a trailer for a forthcoming film by Dutch lawmaker Geert Wilders, which portrays Islam in a negative light, was behind the ban.

"They asked us to ban it immediately... and the order says the ban will continue until further notice," said Wahaj-us-Siraj, convener of the Association of Pakistan Internet Service Providers.

"Users are quite upset. They're screaming at ISPs which can't do anything.

"The government has valid reason for that, but they have to find a better way of doing it. If we continue blocking popular websites, people will stop using the internet."

Other countries that have temporarily blocked access to YouTube include Turkey and Thailand.