The Islamic state tightened its cyber security after its disputed nuclear programme was attacked in 2010 by the Stuxnet computer worm, which caused centrifuges to fail at the main Iranian uranium enrichment facility.
Tehran, whose nuclear programme is suspected by the West of being aimed at developing a bomb, accused the United States and Israel of deploying the worm.
"In recent days, all governmental agencies and offices have been connected to the national information network," deputy communications and technology minister Ali Hakim-Javadi was quoted as saying on Sunday by the Mehr news agency.
The second phase of the plan would be to connect ordinary Iranians to the national network.
According to Iranian media, the domestic system would be fully implemented by March 2013 but it was not clear whether access to the global Internet would be cut once the secure Iranian system was rolled out.
Millions of websites deemed to have un-Islamic content are blocked by Iranian authorities, along with many expressing anti-government views.
Many Iranians suffered serious problems accessing email and Internet social networking sites in February, ahead of parliamentary elections.
Opposition supporters used social networking sites to organise widespread protests after the disputed 2009 re-election of President Mahmoud Ahmadinejad, which they said was rigged in his favour.
Communications and Technology Minister Reza Taqipour said last month Iran needed to develop its own network to ensure the safety of the country's information, the Fars news agency reported.
"Especially on major issues and during crises, one cannot trust this network at all," he said, referring to the global Internet.
"Control over the Internet should not be in the hands of one or two countries."
Authorities said in April a computer virus was detected inside the control systems of Kharg Island which handles the vast majority of Iran's crude oil exports but the terminal remained operational.
Copyright Thomson Reuters 2012
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