After a slow start, talks between Iran and the six global powers in Vienna to substantiate their nuclear deal entered their second day, signalling that significant hurdles may have to be crossed before tangible progress can be achieved.

A European diplomat was quoted as saying that on Tuesday, participants focused on “the parameters and the process of negotiations, the timetable of what is going to be a medium to long-term process.”

On Wednesday, Helga Schmidt — deputy to the European Union foreign policy chief, Catherine Ashton —chaired the session with Iran’s Deputy Foreign Minister Abbas Araqchi. They were accompanied by senior diplomats from the six global powers — the United States, Russia, China, France, Britain and Germany. The dialogue in the Austrian capital began on a low-key note, mainly on account of the assertion on Monday by Iran’s Supreme Leader Ayatollah Ali Khamenei that talks with the sextet “will lead nowhere.”

Iran’s English language broadcaster, Press TV quoted Ayatollah Khamenei — Iran’s top decision maker —as saying: “The perception of some officials of the former administration and also the present administration [of Iran] is that if we negotiate with the U.S. on the nuclear issue, the problem will be solved. Due to their insistence on negotiations over the nuclear issue, I said I’m not opposed either, but at that time I said that I’m not optimistic.”

On its part, the U.S. Congress is also deeply sceptical about the outcome of the talks. But not entirely sharing the pessimism of his law makers, the U.S. President Barack Obama says that chances of achieving success in the dialogue are fifty-fifty.

Analysts say that Washington is using the talks to fulfil its core objective — of implanting structural impediments that would prevent Iran from making an atomic bomb.

Consequently, the U.S. wants to limit the numbers and sophistication of centrifuges — spinning machines that are used to enrich uranium — in order to prevent Iran from acquiring a sufficient stockpile of material that it can further enrich for making a bomb. Under the nuclear deal signed in November last, Iran is allowed to produce enriched uranium of less than 5 per cent purity, well short of the 90 per cent mark that is required for developing a nuclear warhead. Iran had also agreed to dilute or turn into oxide, its existing 20 per cent stocks , negating the possibility of weaponisation.