Iran is giving up some "voluntary commitments" to the six-nation nuclear deal, but is not pulling out of the deal, Foreign Minister Mohammad Zarif says.
Iranian state media quote Zarif as saying Iran is making the move because "the European Union and others ... did not have the power to resist U.S. pressure."
Zarif did not specify what he means.
But a newspaper tied to the hardline Revolutionary Guard says Wednesday's announcement would "ignite the matchstick for burning the deal."
President Hassan Rouhani will send letters to Britain, China, France, Germany, and Russia outlining exactly which parts of the deal he is abandoning.
He also plans to make a speech Wednesday.
His remarks will come exactly one year after President Donald Trump pulled the U.S. out of the agreement, calling it one of the worst deals ever put together.
A French official cautions Iran against making any moves that would compel Europe and others to reimpose sanctions.
"Depending on what is in the statement from Tehran, at this stage what we're expecting is a collective European reaction. But as we do not yet know exactly what will be in it, we are preparing for different eventualities," the official said Tuesday.
The 2015 agreement obligated Iran to reduce its uranium enrichment program in exchange for sanctions relief.
The U.S. reimposed sanctions on Iran when Trump tore up the deal. The sanctions have had a devastating effect on what was already a weak Iranian economy. The sanctions relief from the five other signatories has brought little help.
The U.S. announced last week it would no longer waive sanctions against countries that buy Iranian oil — another blow to Iran.
Despite the havoc on the Iranian economy, U.N. officials have certified Tehran's compliance with the nuclear deal.
But Iranian newspapers have reported the country could revive some of the nuclear activities it halted under the agreement.