Iran has blocked access to Google's popular and relatively secure Gmail service today amid first steps by the Islamic republic to establish a walled-off national intranet separate from the worldwide internet.

Access to Google's search page was also restricted to its unsecured version, web users in Iran found. Attempts to access it using a secure protocol were also blocked.

The curbs were announced in a mobile phone text message quoting Abdolsamad Khoramabadi, an adviser to Iran's public prosecutor's office and the secretary of an official group tasked with detecting internet content deemed illegal.

"Due to the repeated demands of the people, Google and Gmail will be filtered nationwide. They will remain filtered until further notice," the message read.

Google's own website tracking country-by-country access to its services did not immediately reflect the blocks.