A government deputy minister announced the ban Sunday on state television, the BBC reported.
The restriction follow protests in the Muslim world, including some in Iran, against an anti-Islamic film posted on Google's video-sharing site YouTube.
"Google and Gmail will be filtered nationwide, and will remain filtered until further notice," Abdul Samad Khoramabadi, an adviser to Iran's public prosecutor's office, said.
It is not the first time Iranian authorities have cut access to Google services.
"Google search website is accessible, but is not functioning properly," the BBC's Persian service reported. "Google services which need a secure SSL [Secure Sockets Layer] connection are out of reach in Iran."
The unsecured version of the search engine remains accessible but is much more vulnerable to government eavesdropping, the service said.
"This is just a move by the Iranian government 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," Mahmood Tajali Mehr, an Iranian telecommunications consultant living in Germany, said.
"But every schoolchild knows how to bypass restrictions by using VPNs (virtual private networks), it's very common in Iran," he said, adding he did not think the restrictions would be in place for long.
"This is just a propaganda tool to demonstrate that Iran is doing something against the United States, but it is unlikely to last longer than a few days," he said.