The board of the International Atomic Energy Agency will hear a report by its Director-General Mohamed ElBaradei. The council could move to impose economic and political sanctions on the Islamic republic. Iran said on Sunday if it was reported to the Security Council full-scale uranium enrichment would resume.
Western powers believe Iran wants to develop nuclear weapons, for which enrichment is a key process, but Tehran says its plans are for civilian energy. The IAEA has demanded that Iran suspend nuclear enrichment completely. Iran refuses, maintaining it is its sovereign right.
"The Iran regime must be made aware that if it continues down the path of international isolation, there will be tangible and painful consequences," US Ambassador to the UN John Bolton said on Sunday.
But Iran remained defiant. Nuclear negotiator Ali Larijani told a news conference in Tehran: "If Iran's nuclear dossier is referred to the UN Security Council, [large-scale] uranium enrichment will be resumed.
"If [the US and its allies] want to use force, we will pursue our own path." Mr Larijani added: "Going to the Security Council will certainly not make Iran go back on research and development."
The IAEA meeting in Vienna - expected to last several days - will discuss a report on Iran by the agency's director general, Mohamed ElBaradei, though this might not happen until Tuesday or Wednesday.
The report, which was leaked to the media earlier this week, says the Iranians have begun feeding uranium gas into centrifuges - a first step in a process that can produce fuel for nuclear reactors or bomb material. It also says Tehran has rejected stricter inspections, and has hindered inspectors' work.
Three years of negotiations between Iran and the EU, and the latest round of talks between Moscow and Tehran, have brought no significant result.
Ali Larijani said Iran would go its own way
However BBC world affairs correspondent Paul Reynolds says sanctions are still a long way off and might never come.
Warnings and demands that Iran should suspend its nuclear programme will in any case come first, our correspondent adds.
Russian and China - permanent members of the Security Council with the power of veto - have so far opposed imposing sanctions on Iran.
Chinese Foreign Minister Li Zhaoxing said on Sunday he still had not lost hope that negotiations would work.
"China hopes Iran can as soon as possible resume negotiations with the European Union and negotiations with Russia. The important thing is to peacefully and properly resolve the problem through diplomatic means," he said.
Iran announced in January that it was resuming uranium enrichment research, ending a two-year-old suspension it had agreed to with the UK, France and Germany.Güncelleme Tarihi: 20 Eylül 2018, 18:16