Iran is entering talks with six world powers over its nuclear programme this week with good intentions, the Islamic Republic's chief nuclear negotiator has said.
Saeed Jalili, who is attending the talks in Geneva on Thursday, described the meeting as an "opportunity and a test" for those attending and said "we are entering the talks with good will".
The United States and its Western allies have made clear they will focus on Iran's disputed nuclear programme, which they suspect is aimed at making bombs, at the meeting.
On Tuesday, Ali Akbar Salehi, the head of Iran's Atomic Energy Organisation, said "we are not going to discuss anything related to our nuclear rights" at the talks between Iran and the US, Russia, China, Britain, France and Germany.
Speaking before boarding his flight to Switzerland at Tehran's international Imam Khomeini airport, Jalili said: "Iran's national, regional and international capacities ... could be an opportunity for creating a world based upon peace, justice and progress."
Tehran has offered wide-ranging talks on security and other issues, but repeatedly ruled out any discussions about its "nuclear rights" at the meeting, the first since Barack Obama, the US president, took office
Robert Gibbs, a White House spokesman, said the US would bring up its concerns on uranium enrichment, even if Tehran refuses to discuss the issue with the five permanent members of the UN Security Council and Germany.
Washington has suggested possible new sanctions on banking and the oil and gas industry if Iran, the world's fifth-largest crude exporter, fails to assuage Western fears it seeks nuclear weapons.
Speaking to Al Jazeera, Martin Navias, a senior research associate at the Centre for Defence Studies in London, said: "I think the Americans and the Europeans by themselves can increase the pain on Iran, there is no question of that.
"They can sanction companies dealing with Iran's import of gasoline products, they can increase the insurance rates and do a number of things by themselves.
"But to make sanctions really effective, really impose costs on the Iranian government, they have to bring the Russians and the Chinese in.
"And I know the Russians have recently been saying that they were more willing to go along with sanctions, but I'm not sure this has any real meaning, and the Chinese, on the other hand, have indicated quite categorically that they want to slow down any talk of sanctions."
Iran, has denied it is developing a nuclear weapon and says it needs nuclear technology to generate electricity.
In his remarks on Tuesday, Salehi said: "We can discuss about disarmament, we can discuss about non-proliferation and other general issues."
But he ruled out any discussion of the country's second uranium enrichment plant.
Tehran disclosed the second plant to the UN nuclear watchdog last week after Western intelligence agents reportedly discovered its existence.
"The new site is part of our rights and there is no need to discuss it," Salehi said.
There have been reports that Iran's parliament may advocate Tehran's withdrawal from the nuclear Non-Proliferation Treaty (NPT) if talks with the world powers fail and the US keeps putting pressure on Iran.
In an interview carried by Iran's state Press TV on Wednesday, Hassan Ghafourifard, an Iranian MP, said: "If the P5+1 [six world powers] continues to talk with us with the language of force to push us into a corner, and to talk about more sanctions, there might be no choice but to step out of the talks.
"If things go from bad to worse, then we might take more action on that ... like withdrawing from the NPT."
Top Iranian officials have repeatedly said Tehran has no intention to leave the NPT, under which its nuclear facilities are subject to regular UN nuclear watchdog inspections, or seek nuclear weapons it says violate the tenets of Islam.
Strategic analysts believe Iran would think twice before quitting the NPT since such a move would betray nuclear weapons ambitions and could provoke pre-emptive attack by Israel and possibly the United States.
Ministers from the world powers are holding preparatory talks in Geneva on Wednesday ahead of the meeting with Iran.