EU Energy Commissioner Miguel Arias Canete arrived in Tehran on Saturday to present plans for continuing oil and gas purchases and protect European companies despite renewed US sanctions on Iran.
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 at a press conference alongside Iran's Atomic Energy Organisation head Ali Akbar Salehi.
"We will have to ask for waivers, for carve outs for the companies that make investments."
Canete, the first Western official to visit Iran since the US decision, was due to meet Environment Minister Isa Kalantari and Oil Minister Bijan Namdar Zanganeh later on Saturday, and Foreign Minister Mohammad Javad Zarif on Sunday.
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.
European leaders have vowed to maintain the deal and introduce measures to encourage trade and protect EU firms from US sanctions.
But several of their companies -- including France's Total and Holland's Maersk -- have already said it will be impossible to stay in Iran once US sanctions are fully reimposed over the next six months, unless they receive explicit exemptions from Washington.
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.