The European Commissioner for Energy and Climate, Miguel Arias Canete, delivered the message during a visit to Tehran and also said the 28-nation EU, once the biggest importer of Iranian oil, hoped to boost trade with Iran.
“We have sent a message to our Iranian friends that as long as they are sticking to the (nuclear) agreement the Europeans will... fulfill their commitment. And they said the same thing on the other side,” Canete said at a press conference alongside Atomic Energy Organization of Iran head Ali Akbar Salehi.
Canete said preserving the 2015 nuclear deal, despite the US decision to withdraw, was "fundamental for peace in the region".
"For sure there are clear difficulties with the sanctions," Canete said.
"We will have to ask for waivers, for carveouts for the companies that make investments.
“We will try to intensify our flows of trade that have been very positive for the Iranian economy,” he said.
Salehi acknowledged Europe's efforts to maintain the nuclear deal.
"We see the European Union... is making an extensive effort. They have promised to do so, and God willing, they will put that into practice," Salehi told reporters.
He said his country hoped the EU would manage to salvage the deal, in which Tehran agreed to curb its nuclear program in return for the lifting of Western sanctions.
“We hope their efforts materialize... America’s actions... show that it is not a trustworthy country in international dealings,” Salehi told the joint news conference in Tehran.
Since Trump’s announcement on May 8 about the US exit, 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, echoing Iran’s official stance, ruled out any possibility of renegotiating the accord.
He 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.
Under the 2015 deal, Iran’s level of enrichment must remain at around 3.6 percent. Iran stopped producing 20 percent enriched uranium as part of the agreement.
“Unfortunately because of the negative interferences of the US, we were not able to reap the fruits of the JCPOA (Joint Comprehensive Plan of Action) we expected,” Salehi said.
“So the public opinion is not as supportive as it was before and if the other side does not deliver... we will keep losing the support of our people for the JCPOA.”
European leaders have vowed to maintain the deal and introduce measures to encourage trade and protect EU firms from US sanctions.
On Friday, the European Commission launched the process of activating a law that bans European companies from complying with US sanctions against Iran and does not recognize any court rulings that enforce American penalties.
“As the European Commission we have the duty to protect European companies. We now need to act and this is why we are launching the process of to activate the ‘blocking statute’ from 1996. We will do that tomorrow morning at 1030,” European Commission President Jean-Claude Juncker said on Thursday.
“We also decided to allow the European Investment Bank to facilitate European companies’ investment in Iran. The commission itself will maintain its cooperation will Iran,” Juncker told a news conference after a meeting of EU leaders.
Iran's trade with the European Union is around 20 billion euros, evenly split between imports and exports.
The vast majority of EU purchases from Iran – 90 percent – is oil purchases, going primarily to Spain, France, Italy, Greece, the Netherlands and Germany.
Iran, which has the world's fourth-biggest oil reserves, produces some 3.8 million barrels of oil per day, 70 percent of which goes to China and other Asian countries, and 20 percent to Europe.
It also has the second-biggest gas reserves in the world, but limited infrastructure means little is exported.
Russia and China – the other parties to the nuclear deal – have also vowed to maintain trade with Iran, and because they are less exposed to US markets, are less vulnerable to economic pressure from Washington.
Reuters and AFP contributed to this story.