European Union leaders will on Thursday reaffirm their full commitment to the 2015 nuclear deal between Iran and world powers, regardless of whether an increasingly critical United States pulls out.
But the bloc, reluctant to isolate itself completely from Washington, is also looking at whether it should as a next move step up criticism of Iran's ballistic missile program and its role in what the West sees as fomenting instability in the Middle East, a senior EU official said.
President Trump last week adopted a harsh new approach to Iran by refusing to certify its compliance with the nuclear deal, struck with the United States and five other powers including Britain, France, and Germany after more than a decade of diplomacy.
EU leaders will "reaffirms [their] full commitment to the Iran nuclear deal," after talks in Brussels on Thursday, according to a draft statement seen by Reuters.
The EU has been stepping up efforts to save the deal, saying it was crucial to regional and global security, and has appealed to the US Congress not to let it fall.
Mr. Trump has given Congress 60 days to see whether to reimpose economic sanctions on Iran, lifted under the pact in exchange for the scaling down of a program the West fears was aimed at building a nuclear bomb, something Tehran denies.
Should Trump walk away from the deal, Supreme Leader Ayatollah Ali Khamenei said on Wednesday that Iran would "shred" it.
The bloc sees the agreement as a chief international success of recent years, and fears tearing it apart would hurt its credibility as well as harming diplomatic efforts to defuse tensions around another nuclear stand-off, with North Korea.
In outlining his tougher stance, Trump said Tehran must also be held accountable for advancing its ballistic programme and its regional political role.
The EU is at early stages of considering intensifying its criticism of Iran on those issues, something France has been calling for.
"We will defend the nuclear deal and stand by the nuclear deal and implement the nuclear deal. But we also don't want to be standing on a completely opposing side to the US," the EU official said.
"If they withdraw, we would be left in a rather interesting company with China and Russia. So there may be an issue of separating the nuclear deal from the ballistic programme and Iran's regional role, sending signals on the latter two."
The EU has stepped up contacts with the US Congress.
"They were never very fond of the nuclear deal in the first place but now the situation has changed a lot, both many Democrats as well as some Republicans feel like they need to play a more active role on foreign policy to restrain the president," the official added.
Iran's elite Islamic Revolutionary Guards (IRGC) said on Thursday the ballistic missile program would accelerate despite US and EU pressure to suspend it, the semi-official Tasnim news agency reported.
This story was reported by Reuters.