The European Union is resuming trade talks with Iran, 18 months after they were halted over Tehran's nuclear programme.
Iran has been accused of keeping some of its nuclear activities secret
Negotiations are restarting after Iran's agreement in November to suspend the enrichment of uranium.
The European Commissioner for External Relations said the resumption of talks was a clear signal that the EU wished to work with Iran.
Discussions in Brussels will also encompass human rights and security.
The Iran-EU trade talks, which were launched in December 2002, were suspended in mid-2003 amid mounting tensions, particularly over Tehran's refusal to allow snap inspections of its nuclear facilities.
But despite the latest move, tension remains.
Tehran has agreed to maintain the suspension of its uranium enrichment activities only as long as the EU trade talks continue.
Iran maintains that its nuclear program is strictly civilian and peaceful and that it is not developing atomic weapons.
But the United States wants the IAEA to take Iran to the United Nations Security Council for possible sanctions over what Washington says is a covert nuclear weapons program.
Also on Wednesday, officials from Iran and Russia are due to sign a deal on the construction of a big new hydro-electric power station in Tajikstan.
The BBC Central Asian correspondent says the Iranians and Russians are planning to develop the power station as one of a chain which would stretch through the mountains near the Afghan border.