The US has SLOTXO taken down dozens of Iranian and Iran-linked news sites which it accuses of spreading disinformation.
The sites were replaced on Tuesday with notices saying they had been "seized" as part of a law enforcement action. They included Iran's state-run English-language channel, Press TV.
Several were back online within hours with new domain addresses.
Iran criticised the seizures and warned that they were "not constructive" for talks aimed at reviving a nuclear deal.
The US Department of Justice said in a statement that it had seized 33 websites used by the Iranian Islamic Radio and Television Union (IRTVU) and another three run by the Iran-backed Kataib Hezbollah militia in Iraq in violation of US sanctions.
The sites had been used by components of the Iranian government "disguised as news organizations or media outlets" to target the US "with disinformation campaigns and malign influence operations", it alleged.
The justice department said IRTVU was subject to sanctions because it was owned or controlled by the Islamic Revolutionary Guard Corps, which the US designated as a foreign terrorist organisation in 2019.
The domains IRTVU was using were owned by a US company and it had not obtained a license from the US Treasury's Office of Foreign Assets Control prior to using them, it added.
Kataib Hezbollah is also a US-designated foreign terrorist organisation.