Matthew Tueller and two other US diplomats in Iraq "have effectively engaged in organising, financing, leading and committing terrorist acts against the interests of the government or citizens" of Iran, the foreign ministry said in a statement released on Twitter.
It also accused them of being involved in the killing of top Iranian general Qassem Soleimani by a US drone strike near Baghdad's airport in January, "support for extremist and terrorist groups", and implementing US sanctions against the Islamic republic.
The two other diplomats are Tueller's deputy Steve Fagin and Rob Waller, head of US consulate in Arbil, the capital of Iraq's northern Kurdistan region.
"Anti-Iran moves won't go unanswered," Iran's foreign ministry spokesman Saeed Khatibzadeh wrote on Twitter with the statement attached.
Washington on Thursday slapped new sanctions on five Iranian entities over "brazen attempts" to interfere with the November 3 US election, with Tehran strongly denying the accusations.
The US also separately blacklisted Tehran's envoy to Baghdad Iraj Masjedi, describing him as a "close adviser" to Soleimani.
In response, Masjedi told state media he was "pleased to hear the news" that the "terrorist and criminal regime of the United States has put me once more on the list of its unjust sanctions alongside 80 million Iranians".
Tensions between arch-enemies Tehran and Washington have increased since US President Donald Trump withdrew from a landmark nuclear agreement with Tehran and world powers and reimposed punishing sanctions.
They flared in January when a US drone strike killed Soleimani, who headed the Qods Force of Iran's Revolutionary Guards.
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