With every passing month the international dispute over Iran's nuclear programme becomes more intractable.

On the one side, the West and Israel are convinced that Iran is working towards a nuclear weapon and are determined that this should never be allowed to become reality - even if that ultimately means taking military action to prevent it. On the other side, Iran insists that its nuclear project is purely peaceful and that its controversial uranium enrichment programme is aimed only at producing fuel for the Iranian economy and medical isotopes for use in its health services. 

Definitive evidence in support of either claim is hard to find and what evidence there is is often disputed. Nevertheless the UN's International Atomic Energy Agency (IAEA) has long expressed concern about Iran's nuclear programme. In November 2011, for example, it reported that Iran had carried out activities "relevant to the development of a nuclear explosive device". It said that its investigations had uncovered alleged Iranian testing of explosives, experiments on detonating a nuclear weapon, and what appears to be work on 'weaponisation' - the processes by which a nuclear device could be adapted to fit into a rocket or missile. It also said that Iran may have used computer modelling to look at how effective a nuclear device would be. 

Some of these activities, one might think, could only be of relevance to a nuclear weapons programme, but the agency has never said definitively that Iran has mastered the process, nor has it said how long it would take Iran to make a bomb, should that be its ultimate aim. 

Iran's response to these allegations has not wavered. It insists that all the claims are politically motivated and that it is simply doing what it is entitled to do as a sovereign state and as a signatory to the Nuclear Non-Proliferation Treaty (NPT). It says it is the victim of an Israeli and US-led conspiracy and points to the unexplained murder of five of its top nuclear scientists in the last two years. The most recent of these came in January this year, when Iranian nuclear physicist Mostafa Ahmadi-Roshan was killed after two men on a motorcycle attached a magnetic bomb to his car. It later emerged that he was on his way to a ceremony commemorating the death of one of his colleagues, Masoud Ali Mohammadi, who was assassinated in January 2010 in front of his home by a bomb attached to a motorcycle. 

Nevertheless, as tension escalates, the position of both sides has hardened. On a recent visit to the US to discuss the issue with Barack Obama, the US president, Binyamin Netanyahu, the Israeli prime minister, publicly restated Israel's position - that it reserves the right to defend itself against the threat from Iran. In turn, Mahmoud Ahmadinejad, the Iranian president, has said: "The Iranian nation will not succumb to bullying, invasion and the violation of its rights."

Neither statement does much to diminish international anxiety that one day soon this issue might end in Israeli or US airstrikes on Iranian facilities such as the Natanz nuclear reactor - which could turn lead to retaliation from Iran and another war in the Middle East.

So is Iran really building a nuclear weapon or are its activities peaceful as it claims? Would Israel really attack Iran's nuclear facilities and why is it so determined to remain the only country in the region with the bomb? This episode of People & Power looks at the background to a dispute taking place against much sabre-rattling but in which the truth is harder to pin down.

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