British Foreign Secretary Boris Johnson speaks during a news conference with, from left, French Foreign Minister Jean-Yves Le Drian, German counterpart Sigmar Gabriel and European Union foreign policy chief Federica Mogherini after meeting Iranian Foreign Minister Mohammad Javad Zarif in Brussels. (Francois Lenoir/Reuters)

Top European diplomats offered Iran's foreign minister renewed support Thursday for the landmark 2015 nuclear deal with Tehran even as the White House weighs whether to step away from the pact.

But the European envoys also questioned Mohammad Javad Zarif over contentious matters such as Iran's missile program and its role in Syria's war as a key ally of President Bashar al-Assad.

The messages from the foreign ministers of France, Britain and Germany sought to acknowledge the range of Western concerns, including Iran's ballistic missile development and its crackdown on dissent after street protests in the country this month.

But Europe also signaled its opposition to the Trump administration over the nuclear deal, which ended most international sanctions on Iran in exchange for curbs on its nuclear program.

"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," the European Union's foreign policy chief, Federica Mogherini, said after the talks in Brussels.

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

Officials in the administration have suggested that the president plans to extend the waivers that lifted sanctions on Iran but could seek new measures over issues such as human rights and Tehran's missile program. This was first reported by the Associated Press.

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

In October, Trump declined to certify that the agreement was in U.S. national security interests despite reports by the U.N. nuclear agency and others that Iran was abiding by the terms of 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.

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

The meeting was the Iranian foreign minister's first face-to-face dialogue in the West since a wave of unrest was touched off by frustrations over Iran's stumbling economy. Among the protesters' grievances was the failure of the nuclear accord to quickly boost the Iranian economy, as promised by the deal's key backers, including President Hassan Rouhani.

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

European firms have moved quickly to reestablish business ties after the nuclear deal, with aviation and carmaking firms leading the way. Europe's Airbus consortium has reached a deal to sell up to 100 airliners to state-run Iran Air. Some industry experts put the value of the deal at more than $16 billion.

Airbus rival Boeing also has sealed an agreement, estimated to be worth as much as $20 billion, to sell Iran Air up to 80 aircraft. The Boeing plans have been thrown into question by Trump's opposition to the nuclear pact, but Iran Air's chief, Farzaneh Sharafbafi, told Iranian media in October that the sale could go through even if the United States abandoned the nuclear accord.