It has been exactly a year since the last UN security council resolution imposed extra sanctions on Iran. International debate is resuming on the country's continued failure to heed UN decisions, and a new report by the International Atomic Energy Agency rightly draws attention to the questions Iran has not answered about experiments it has made on nuclear bomb technology.

As ambassadors to Iran during the past decade, we have all followed closely the development of this crisis. It is unacceptable that the talks have been deadlocked for such a long time.

The Arab world and the Middle East are entering a new epoch in which no country is immune from change. The Islamic Republic of Iran faces the disaffection of a significant part of its population, and this period of uncertainty offers opportunities to reconsider the west's established position on the nuclear question.

In terms of international law, the position of Europe and the United States may be less assured than is generally believed. Basically, it is embodied in a set of security council resolutions authorising coercive measures in case of "threats to the peace".

But what constitutes the threat? Is it the enrichment of uranium in Iranian centrifuges? This is certainly a sensitive activity, in a highly sensitive region. The international community's concerns are legitimate and Iran has a moral duty to answer them. In principle, however, nothing in international law or in the non-proliferation treaty forbids uranium enrichment. Several other countries, parties or not to the treaty, enrich uranium without being accused of "threatening the peace". And in Iran, this activity is submitted to inspections by the IAEA inspections. These inspections, it's true, are albeit constrained by an agreement on safeguards dating from the 70s. But the IAEA has never uncovered any attempted diversion of nuclear material to military use.

So is Iran attempting to build a nuclear weapon? For at least three years, the US intelligence community has discounted this hypothesis. The US director of national intelligence, James Clapper, testified last February to Congress: "We continue to assess [whether] Iran is keeping open the option to develop nuclear weapons … We do not know, however, if Iran will eventually decide to build nuclear weapons."

Most experts, even in Israel, view Iran as striving to become a "threshold country", technically able to produce a nuclear weapon but abstaining from doing so for now. Again, nothing in international law forbids this ambition. Several other countries are close to, or have already reached, such a threshold, with a commitment not to acquire nuclear weapons. Nobody seems to bother them.

We often hear that Iran's refusal to negotiate seriously left our countries no other choice but to drag it in 2006 to the security council. Here too, things are not quite that clear. In 2005 Iran was ready to discuss an upper limit for the number of its centrifuges and to maintain its rate of enrichment far below the high levels necessary for weapons. Tehran also expressed its readiness to allow intrusive inspections, even in non-declared sites. But at that time Europe and the US wanted to compel Iran to ditch its enrichment programme entirely.

Iranians assume that this is still the European and US goal, and that for this reason the security council insists on suspension of all Iranian enrichment activities. But the goal of "zero centrifuges operating in Iran, permanently or temporarily" is unrealistic, and has contributed greatly to the present standoff.

Some may ask why we should offer the Iranian regime an opening that may help to restore its internal and international legitimacy. Should we not wait for a more palatable successor? It's a legitimate question, but we shouldn't overestimate the influence of nuclear negotiation on internal developments in Iran. Ronald Reagan used to call the USSR the "evil empire", but that did not stop him from negotiating intensely with Mikhail Gorbachev on nuclear disarmament.

The failure of the last round of negotiation in January shows that the current deadlock will be difficult to break. The more discreet and technical negotiations are, the better chance they will have to progress. And we already know that any solution will have to build on the quality of the inspection system. Either we trust the IAEA's ability to supervise all its member states, including Iran, or we do not. And if we do not, we must ask why, if the organisation is effective only with its most virtuous members, we should continue to maintain it.

The next step should be for the two sides in this conflict to ask the IAEA what additional tools it needs to monitor Iran's nuclear programme fully, and to provide credible assurances that all its connected activities are purely peaceful. The agency's answer would offer a basis for the next round of pragmatic negotiations.

• This article was co-written by Richard Dalton and five other former ambassadors to Iran: Paul von Maltzahn (Germany), Steen Hohwü-Christensen (Sweden), Guillaume Metten (Belgium), François Nicoullaud (France) and Roberto Toscano (Italy)