The US embassy in Tehran has been closed for more than three decades, but now an online equivalent offers services including visa information, BBC reported.
The "virtual embassy" went online on Tuesday in English and Farsi, but the US says it is not intended to replace an official diplomatic mission to Iran. In a statement, the state department said the virtual embassy should "work as a bridge" between America and Iran.
Announcing the opening of the virtual embassy, the US stressed that dialogue between Americans and Iranians remained essential.
"Because the United States and Iran do not have diplomatic relations, we have missed some important opportunities for dialogue with you, the citizens of Iran," Secretary of State Hillary Clinton said in a video message uploaded to the site.
The US embassy was closed when militants stormed the premises and seized 52 American hostages in 1979. That sparked a crisis which endured for 444 days.
Earlier this year, the state department launched a Farsi-language Twitter account and Facebook page aimed at Iranians.