Britain, France, and Germany are expected to announce the launch of a financial mechanism designed to help European companies trade with Iran without facing US sanctions on Friday.
The financial vehicle, known as INSTEX, has been in preparation for nearly six months. European diplomats flew to Tehran last week for three days of talks on the technical details.
It was unclear on Wednesday whether making it operational will be enough to persuade Iran not to breach its nuclear deal commitments.
The remaining members of the nuclear deal will also meet in Vienna on Friday to discuss the implications of an Iranian violation of its obligations.
The president of Iraq warned on Wednesday that he would not allow his country to become a theatre in a US-Iranian proxy war.
Bahim Salih said he had warned both the US and its allies and Iran that Iraq would not allow its territory to be used to attack the other side. “We are asking everybody to cool it down,” Mr Salih said in a speech in London.