The Trump administration declared that UN sanctions on Iran have been restored in a move viewed as illegal by most other countries.
The announcement comes ahead of the UN General Assembly on Tuesday and will likely result in a showdown at the meeting of nations.
The administration said the sanctions would take effect on Saturday, since it had been 30 days since Secretary of State Mike Pompeo notified the security council that Iran was in “significant non-performance” of its obligations under the 2015 nuclear deal, known as the Joint Comprehensive Plan of Action (JCPOA).
But most countries have said that the Trump administration cannot call for a snapback of sanctions after withdrawing from the Iran deal in 2018.
Britain, France and Germany said in a statement released on Sunday that the US withdrawal from the deal means "that any decision or action taken on the basis of this procedure... are without effect in law.”
The Iranian government spokesman said the snapback sanctions have only happened in “the fantastical world” of the Trump administration, stating that no one else was buying the move.
The US announcement, however, pushed the Iranian currency down to its lowest level ever on Sunday.
Iranian President Hassan Rouhani said that the Trump administration's "maximum pressure" campaign had turned into "maximum isolation" for the United States, according to AFP.
It remains unclear how the US administration will ensure the sanctions are enforced when even European allies say the move is illegal. European countries still hope to preserve the nuclear deal.
Trump plans to address Iran in a speech to the General Assembly's annual high-level meeting on Tuesday.