US President Donald Trump is set to announce whether he will pull out of the Iran nuclear deal or stay in and work with European allies who have struggled to persuade him it has successfully halted Iran's nuclear ambitions.
Trump has consistently threatened to pull out of the 2015 agreement because it does not address Iran's ballistic missile program or its role in wars in Syria and Yemen, and does not permanently prevent Tehran from developing nuclear weapons.
European leaders have warned that a US withdrawal would undo years of work that led to and sustained a landmark deal that has kept nuclear weapons out of Iran's hands.
It could also ratchet up tensions in a region riven with interrelated conflicts, including the multi-layered conflict in Syria where Iran's presence has brought it into conflict with Israel. It will also impact oil markets due to Iran's role as a major exporter.
"This deal ... is a factor of peace and stabilisation in a very eruptive region," French Defence Minister Florence Parly told RTL radio.
Trump, in a tweet on Monday, said he would make the announcement at 2pm (1800 GMT) on Tuesday.
Iran suggested its economy would not be hurt whatever happened, but its rial was near record lows against the dollar in the free market as Iranians tried to buy hard currency, fearing financial turmoil if Trump quits the deal.
"One man in one country might create some problems for us for a few months, but we will overcome those problems," President Hassan Rouhani said in televised remarks.
"If we are under sanctions or not, we should stand on our own feet. This is very important for the development of our country," Rouhani said.
A senior US official close to the process said France, Germany and Britain had moved significantly to address Trump's concerns over the ballistic missile program, the terms under which international inspectors visit suspect Iranian sites and "sunset" clauses under which some terms of the deal expire.
The Iran deal, negotiated during the administration of Trump's Democratic predecessor, Barack Obama, eased economic sanctions on Iran in exchange for Tehran limiting its nuclear program.
Trump has called it the "worst deal ever negotiated" and he wants Britain, France and Germany - which also signed the pact along with Russia and China - to toughen up the terms.
British Foreign Secretary Boris Johnson made the rounds in Washington on Monday, including talks with Vice President Mike Pence and Secretary of State Mike Pompeo.
Still, European diplomats privately said they expected Trump to withdraw from the agreement.
Iran has threatened to retaliate if the US pulls out, although it has not said how. Diplomats and military experts say Tehran could seek to resume its nuclear arms program or step up its military involvement in Iraq, Syria, Yemen and Lebanon.
The Kremlin said on Tuesday the withdrawal of the US from the Iran nuclear deal would have harmful consequences.
Rouhani suggested on Monday that Iran might remain in the nuclear deal even if Trump abandons it and imposes sanctions. But he also warned that Tehran would fiercely resist US efforts to limit its influence in the Middle East.
