Europe Correspondent Paul Cunningham continues his reports from Tehran ahead of the start of talks to conclude a deal on Iran's nuclear programme.

As a light dusting of snow drifted down on the Iranian capital, Tehran, the country's chief nuclear negotiator was making an effort to speak to me, but finding it difficult.

Though his voice was barely audible due to a "serious cold", Mohammad Javad Zarif's message was clear - he said he believed it would be "easy" to reach a final and comprehensive deal with the West on Iran's nuclear programme, and that it would be reached "this year".

However, as our interview progressed, Minister Zarif qualified his message. He said: "If the two sides are serious, and we negotiate in good faith... it's easy to reach an understanding, and to succeed reaching a complete solution."

Then came the oft-quoted line: "Iran does not seek nuclear weapons."

The difficulty for Mr Zarif, and for Iran, is that such a declaration will not be taken at face value by the six countries on the other side of the negotiating table in Geneva.

A deep suspicion remains that Iran's nuclear power programme is a cover to secure a nuclear weapons capacity.

Consequently, Germany, France, Britain, the US, Russia and China have been using the 'v' word a lot - they want independent inspectors to 'verify' that efforts are not being made to build a bomb.

For months, the two sides negotiated an interim arrangement, which will see some sanctions on Iran being lifted in return for a significant reduction of its nuclear programme. It will signal the beginning of a six-month deadline for talks on a comprehensive deal to be completed.

The whole process has now reached a critical juncture - that interim deal is due to come into effect on 20 January, and so the deadline clock will begin to tick.

Speaking to RTÉ, Mr Zarif appeared anxious that the talks would be concluded well within the six-month deadline.

He said: "We do not have all the time in the world. We have opponents of engagement that are particularly operative in the United States and elsewhere. People who seek conflict and tension."

That was a dig aimed mainly at politicians in the US Congress, particularly on the Republican side, who are considering increasing sanctions on Iran.

Iran certainly has given considerable ground in the interim deal, and this will have major impacts at its three facilities at Fordow, Arak and Natanz.

The details are highly technical but the process whereby uranium is enriched to make it usable in nuclear plants - or weapons - will be severely restricted. And inspectors will be allowed to ensure that fuel will not be produced, tested, or transferred to the Arak nuclear power plant.

In exchange for fulfilling these conditions, Iran will receive relief from sanctions, such as being allowed to sell more oil, something which is estimated to be worth around €4 billion to the Iranian economy.

While the additional income will be a shot in the arm to Iran's faltering economy, Mr Zarif was dismissive of sanctions themselves.

Asked if the country could buckle under new sanctions in the event of a deal not being reached, he declared: "We have lived with sanctions for many years. We can continue to live without them."

Hardening his tone, he ridiculed the sanctions regime: "When these sanctions started, we had 700 centrifuges [used to enrich uranium]. Now we have 19,000. They are an abject failure."

Mr Zarif also warned: "The West should remember that the Iranian people require and demand respect for their rights; respect for their dignity; respect for their choice."

The minister's message was a more diplomatic version of what the Iranian Supreme Leader, Ayatollah Seyed Ali Khamenei, said last week.

Iran News quoted him as saying "When the enemy encounters a resolved and resistant nation, it will have no way but to retreat. The assumption that the Iranian nation came to the negotiation table under the pressure of sanctions is an absolute mistake."

He added: "One of the good results of the recent nuclear negotiations was that the hostility of the US officials toward Iran and the Iranians and Islam and the Muslims was revealed."

Maybe it will not be so "easy" to conclude a deal in six months after all.