These are the first such talks in more than a year, although analysts say any breakthrough is unlikely.
On Sunday Iran said it had delivered its first domestically produced raw uranium and would now go into the talks with “strength and power”.
Western powers fear Iran may be trying to produce nuclear arms, but Tehran says its programme is purely peaceful.
On Iranian state television, nuclear chief Ali Akbar Salehi said the Geneva talks were for the benefit of the other countries, not Iran.
“We want to create a graceful solution out of the political deadlock for those who have pressurised us,” he said.
Iran’s top nuclear negotiator Saeed Jalili is meeting EU foreign affairs chief Catherine Ashton and senior officials from the five permanent members of the UN Security Council – the US, Russia, China, France and Britain – plus Germany.
The talks, being held near the Swiss mission to the United Nations, are scheduled to last for two days. But analysts say the best outcome that can be hoped for is simply the agreement of further meetings.
Continue reading the main story
Paul Reynolds BBC World Affairs correspondent
The resumption of talks with Iran after more than a year is unlikely to mean that Iran is now ready to negotiate a suspension of its enrichment activities as demanded by the Security Council. Indeed, Iran’s announcement just in advance of the talks that it is now able to produce its own yellowcake, the crushed uranium ore which is turned into a gas for enrichment, has given it a new confidence that it can ride out sanctions.
It might therefore see the talks as an opportunity to restate its position. At the same time it usually wants to show some flexibility on secondary issues, like the supply of fuel for its research reactor which produces medical isotopes.
But at the moment there is stalemate all round. The Wikileaks revelations have shown pressure on the US by its Gulf Arab allies and Israel for military action against Iran but the US has resisted this.
Some Western diplomats and officials involved were downbeat. One was quoted as saying “don’t expect much of anything”, while another added that “it’s going to be very, very boring”.
The last Geneva talks, in October 2009, appeared to agree a breakthrough deal under which Iran would export low-enriched uranium for processing abroad. However, Iran introduced new conditions and the deal foundered.
The UN Security Council has said that until Iran’s peaceful intentions can be fully established, it should stop enrichment and other nuclear activities.
Iran is under four sets of UN sanctions over its refusal to heed repeated Security Council ultimatums to suspend uranium enrichment.
The latest UN sanctions, adopted on 9 June, include a ban on dealing with Iranian banks and insurance companies, as well as steps to prevent investment in Tehran’s oil and gas sector.
Iran says that as a signatory of the Nuclear Non-Proliferation Treaty, it has the right to enrich uranium for fuel for civil nuclear power.
Tension over the nuclear issue was also raised when one of Iran’s top nuclear scientists was killed by a car bomb in Tehran last Monday. Iran blamed Western intelligence services.
Recent Wikileaks releases of secret US diplomatic cables also revealed some Arab states calling for military action against Iran’s nuclear facilities.
On Sunday, Iran said it had mined and produced its first home-manufactured uranium yellowcake.
Saeed Jalili Iran’s negotiator Saeed Jalili is meeting leading EU and UN officials
Mr Salehi said: “The West had counted on the possibility of us being in trouble over raw material but today we had the first batch of yellowcake [raw uranium] from Gachin mine sent to Isfahan [conversion] facility.”
Enriched uranium can be used for fuel in reactors or made into nuclear bombs.
Iran was believed to be running low on its stock of yellowcake, originally imported from South Africa in the 1970s.
Producing it domestically would enable Iran to circumvent the four rounds of increasingly harsh UN sanctions.
White House National Security Council spokesman Mike Hammer said the announcement was not unexpected, as Iran had been trying to develop its own uranium programme for years.
“However… this calls into further question Iran’s intentions and raises additional concerns at a time when Iran needs to address the concerns of the international community,” Mr Hammer said – BBC