BRUSSELS • Top European diplomats have offered Iran's Foreign Minister blanket support for the landmark nuclear deal with Teheran, even as the White House weighs whether to step away from the pact.

But the European envoys also questioned Foreign Minister Mohammed Javad Zarif over disputes such as the country's missile programme and its role in Syria's war as a key ally of President Bashar Assad.

The messages from the foreign ministers of France, Britain and Germany yesterday sought to acknowledge the range of Western concerns, including Iran's ballistic missile development and the crackdowns following street protests across Iran earlier this month.

But Europe also signalled its opposition to the Trump administration over the 2015 nuclear deal, which ended most international sanctions in exchange for curbs on Iran's nuclear programme.

"Unity is essential to preserve a deal that is working, that is making the world safer, that is preventing a nuclear arms race in the region," said the European Union's foreign policy chief, Ms Federica Mogherini, following the talks in Brussels.

President Donald Trump must decide by today whether to continue to back the provisions of the nuclear deal, which effectively opened Iran to international commerce, including a tentative deal with US aircraft maker Boeing.

Officials in the Trump administration have suggested that Mr Trump plans to extend the waivers that lifted sanctions on Iran, but could seek new measures over issues such as human rights and missile programmes.

Such a move would offer some relief in Europe, where leaders fear unilateral US sanctions on Iran could unravel the nuclear deal hammered out between Iran and six world powers.

In October, Mr Trump declined to certify that the agreement was in US national security interests despite reports by the UN nuclear agency and others that Iran was abiding by the deal.

In a statement before the Brussels meeting, British Foreign Secretary Boris Johnson highlighted the sharp break with Washington - calling the nuclear deal "a crucial agreement that makes the world safer".

"There is no indication today that could call into doubt Iranian respect of the agreement," French Foreign Minister Jean-Yves Le Drian told reporters in Brussels.

On Twitter, Mr Zarif posted a message noting "strong consensus in Brussels" that Iran was complying with the nuclear deal and any attempt to undercut the accord was "unacceptable".

The meeting was Mr Zarif's first face-to-face dialogue in the West since a wave of unrest touched off by frustrations over Iran's stumbling economy.

Among the protesters' grievances were complaints that the nuclear accord has failed to quickly boost the Iranian economy as promised by its key backers, including Iranian President Hassan Rouhani.

Yesterday's talks also highlight one of the major points of friction between the US and Europe that could be raised during Mr Trump's visit to World Economic Forum later this month in Davos, Switzerland.

European firms have moved quickly to re-establish business ties after the nuclear deal. European aviation and carmakers have led the way, including a contract with Airbus to sell up to 100 jets to state-run Iran Air. Some industry experts put the value of the deal at more than US$16 billion (S$21.3 billion).

Airbus rival Boeing also sealed an agreement, estimated at US$20 billion, to sell Iran Air up to 80 aircraft.

The Boeing plans have been thrown into question by Mr Trump's opposition to the nuclear pact, but Iran Air's chief, Ms Farzaneh Sharafbafi, told Iranian media last October that she believed the sale could go through even if the US left the nuclear accord.

WASHINGTON POST