For the first time since the deal came into force in 2015, China, Russia, France, Britain and Germany have gathered at Iran's request without the United States, which pulled out on May 8.
Director General of the International Atomic Energy Agency (IAEA) Yukiya Amano has also attended the JCPOA joint commission meeting to reiterate Iran's commitment to its obligations.
IAEA in its 11th periodical report released on Thursday once again verified Iran's adherence to its nuclear deal with world powers.
It was the first report issued by IAEA after US withdrawal from the internationally recognized treaty (JCPOA).
Amano presence is symbolic to show that only the IAEA can confirm a country's breach or commitment to its obligations.
The European Union in a statement had said earlier that the JCPOA joint commission meeting is to study the consequences of the US exit from JCPOA and hold consultations on mechanisms to continue implementation of the deal.
Secretary-General of European External Action Service Helga Schmid chairs the meeting. Iranian Deputy Foreign Minister Abbas Araqchi heads the Iranian delegation to the meeting.
Araqchi arrived in Vienna on Thursday morning and held bilateral meetings with Schmid and head of Russia delegation before start of the JCPOA joint commission meeting.
In reaction to Trump's announcement, EU foreign policy chief Federica Mogherini reiterated EU' cooperation with Iran on the JCPOA. The UK, France, Germany, China and Russia, too, announced that they would stay in the deal.
