The European Union is not doing enough to preserve the benefits for Iran from the 2015 international nuclear pact following the withdrawal of the United States, Iran's foreign minister has told the EU's energy chief.

"With the withdrawal of America, (Iran's) public expectations from the European Union have increased in order to maintain the deal's gains, and in the current context, the European political support for the accord is not sufficient," Mohammad Javad Zarif told Miguel Arias Canete in Tehran, Iran's state news agency IRNA reported.

Since US President Donald Trump announced on 8 May that he would pull the United States out of the deal, EU leaders have pledged to try to keep Iran's oil trade and investment flowing, but conceded that would not be easy.

"We have to preserve this agreement so we don't have to negotiate a new agreement," Arias Canete said after two days of meetings with Iranian officials in Tehran.

"Our message is very clear. This is a nuclear agreement that works."

Under the deal, Tehran agreed to curb its nuclear work in return for the lifting of most Western sanctions.

With the threat of new US sanctions looming over them, some foreign firms have already started signaling their intention to pull back from Iran.

"The announcement of the possible withdrawal by major European companies from their cooperation with Iran is not consistent with the European Union's commitment to implementing (the nuclear deal)," Mr Zarif was quoted as saying.

It comes as three EU sources have denied that diplomats meeting in Vienna on Friday to salvage the Iranian nuclear deal after Washington withdrew will discuss offering Iran financial aid in exchange for concessions.

A German newspaper reported that diplomats from Britain, Germany, France, China and Russia will meet in Vienna on Friday to discuss next steps after the 8 May decision by US President Donald Trump to pull out of a 2015 nuclear accord with Iran.

The 2015 accord between Iran, the US, Russia, China, France, Britain and Germany curbed Iran's nuclear activities in exchange for sanctions relief

The Welt am Sonntag newspaper cited an unnamed senior EU official as saying that the diplomats would discuss a proposal for a new agreement between Iran and world powers that would be the same as the 2015 deal but with some additions to appease the United States.

These could include provisions to address US concerns over Iran's ballistic missile programme and Tehran's support of armed groups in the Middle East, the source said.

"We have to get away from the name 'Vienna nuclear agreement' and add in a few additional elements. Only that will convince President Trump to agree and lift sanctions again," the senior EU official told the paper.

Such an agreement could in the future include financial aid for Iran, the report said.

But three EU sources who were part of negotiations to keep Mr Trump from quitting the nuclear deal told Reuters that this was incorrect.

"The Vienna meeting next Friday will address the implementation issues and details of the JCPOA," one EU source said. "The meeting will not cover any other issues."

No immediate comment was available from the German foreign ministry.

Iran has said it would take part on Friday in a meeting of a joint commission set up by the six world powers, Iran and the European Union to handle any complaints about the deal's implementation.

"On Friday, the joint commission ... will be held at Iran's request, and without the United States, to discuss the consequences of America's withdrawal, and how the remaining countries can continue their commitment to the deal," Deputy Foreign Minister Abbas Araqchi said on state television.

On Monday US Secretary of State Mike Pompeo will outline a "diplomatic road map" and call for broad support from European and other allies to apply pressure on Iran to force it back to the negotiating table, as well as their support to address "the totality of Iran's threats".

Mr Zarif said last week that Iran and European powers have made a good start in talks over how to salvage the deal but much depends on what happens in the next few weeks.