Iran blocked access to YouTube, Google and Gmail over the weekend citing the anti-Islam film that has gained notoriety for allegedly sparking the deadly protests that have spread throughout the Arab world.
According to Iran’s semiofficial Mehr news agency, the sites were restricted "because of public demand."
"Google and YouTube continued to carry the film clip that insulted our people's sacred beliefs," the news agency reported, citing an unnamed source.
A government deputy minister announced the ban on Sunday on state television.
"Google and Gmail will be filtered nationwide, and will remain filtered until further notice," said an adviser to Iran's public prosecutor's office Abdul Samad Khoramabadi.
The announcement was also sent out via text messages.
Kamran Saghafi, of the High Council for the Internet in Iran, warned Iranians not even to try to access the sites.
"Internet users must voluntarily stop using those services and must not even try getting connected, even if it is just to see if they can succeed," the news agency quoted him as saying.
Users can, however, access the sites by using virtual private networks (VPNs), which allow web surfing behind heavily encrypted firewalls.
Many Iranians already use VPNs to bypass the government's restrictions on other blocked Western websites, Mahmood Tajali Mehr, an Iranian telecommunications consultant living in Germany, told the BBC.
"This is just a move by the Iranian governement towards a so-called nationwide intranet, to control all the traffic from the outside, and authorities are saying they will implement it in about three years,” he said.
"But every schoolchild knows how to bypass restrictions by using VPNs, it's very common in Iran," he added.
In February, Iran restricted access to Google and Gmail head of parliamentary elections.
In March, Iran's Supreme Leader, Ayatollah Ali Khamenei, ordered officials to set up a body tasked with monitoring the Internet, called the Supreme Council of Virtual Space.
Iran has also blocked the websites of several Western news agencies and a number of other Internet services, including Facebook and Twitter, are often censored.