The European Union has moved to reassure Iran it remains committed to the nuclear deal, despite Donald Trump's decision to withdraw the U.S. from the accord and reimpose sanctions on the Islamic republic. 

Miguel Arias Canete, the European Commissioner for Energy and Climate, said the 28-nation bloc, once the biggest importer of Iranian oil, also hoped to boost trade with Tehran. 

"We have sent a message to our Iranian friends that as long as they are sticking to the agreement the Europeans will... fulfil their commitment," Canete said during a visit to Tehran on Saturday. "And they said the same thing on the other side."

"We will try to intensify our flows of trade that have been very positive for the Iranian economy."

Iran's nuclear chief, Ali Akbar Salehi, said his country hoped the EU would manage to salvage the 2015 deal, in which Tehran agreed to curb its nuclear program in return for the lifting of most Western sanctions.

"We hope their efforts materialize... America's actions... show that it is not a trustworthy country in international dealings," Salehi told a joint news conference in Tehran.

Since Trump's announcement on 8 May, European countries have said they will try to keep Iran's oil and investment flowing, but have also admitted they will struggle to provide the guarantees Tehran seeks.

Salehi said Iran had several options, including resuming its 20 percent uranium enrichment if the European countries failed to keep the pact alive. He said the EU had only a few weeks to deliver on their promises.

"If the other side keeps itself committed to its promises we also will be keeping ourselves to our promises... We hope the situation will not arise to the point that we will have to go back to the worst option," Salehi told reporters in English.