The European Union (EU) will make sure the nuclear deal with Iran will be continued to be "fully implemented by all parts."
Iran and other countries – the US under the Barack Obama administration, Britain, Russia, France, China and Germany – reached the deal in 2015.
According to the agreement – known as the Joint Comprehensive Plan of Action (JCPOA) – some sanctions against Iran were lifted as long as Tehran curbed its nuclear activity.
EU's Foreign Policy Chief Federica Mogherini said during a conference in Uzbekistan that the agreement was "a major achievement of European and international multilateral diplomacy that is delivering," Reuters reported.
Her comments came weeks after US President Donald Trump refused to re-certify the deal, arguing that Iran was not complying with guidelines and calling the agreement an "embarrassment for the US".
However, the UN nuclear watchdog said on 10 November that Iran was still complying with the deal, AFP reported.
Trump's stance on the deal is likely to jeopardise it. The leader said the possibility of the US pulling out completely from the accord is likely.
The US Congress has until mid-December to decide whether to re-impose sanctions lifted as part of the accord.
Iran warned the US would face consequences if the nuclear deal fails.
Iran's Supreme Leader Ayatollah Ali Khamenei said in October: "The European governments have voiced support for the nuclear deal and condemned the US president's remarks. We welcome their stance, but this is not enough to just ask Trump not rip up the nuclear agreement. The nuclear deal is to their benefit. We will not tear up the agreement as long as the other side remains committed."