The UN blow to Tehran was a heavy one; the Security Council resolution tightened the existing sanctions regime, including a block on Iranian arms exports and an international freeze on the assets of twenty-eight people and organisations involved in Iran's nuclear and missile programmes.

Among the affected organisations are the Sepah-e Pasdaran-e Enghelab-e Islami (Army of the Guardians of the Islamic Revolution, routinely known as the Revolutionary Guards), which represents a major power-bloc in Tehran's complex political scene. The guards are at the sharp end of all the recent confrontations with the west. They are deeply involved in its nuclear and ballistics programme and are accused of interference in Iraq and Lebanon. The measures, adopted in a unanimous vote, give Iran another sixty days to comply with the United Nation's nuclear demands to halt uranium-enrichment activities; if it does not it most likely will face even harsher measures.

A dual power-play

As the tortuous nuclear crisis has dragged on over many months, the Tehran regime has - notwithstanding the odd concessionary gesture - hardened its stance and reaffirmed its national right to pursue civil nuclear energy. During a recent research trip to Tehran, several colleagues explained to me that while this "right" was once perhaps peacefully oriented, today pressure from the international community and encirclement by the United States are pushing the regime in a direction it originally never intended to go.

Indeed, after twenty-seven years of diplomatic deep-freeze with the United States - interspersed with several failed attempts at reconciliation - the theocratic regime seeks one fundamental objective: self-preservation. The chief internal agent in charge of furthering this aim is none other than the Revolutionary Guards. Here, the institutional framework of the Islamic Republic can be said to work in the organisation's favour: while Iran's constitution entrusts the military with protecting Iran's territorial integrity and political independence, it gives the Revolutionary Guards the responsibility of defending the revolution itself.

This is illustrated in the event that by a day preceded the setback to Tehran at the UN: the sudden, surprise seizure of fifteen British marines on 23 March by Iranian Revolutionary Guards for allegedly veering into Iranian waters. The incident is reminiscent of another encounter where eight British servicemen were captured and held for three days in June 2004. That was widely interpreted as muscle-flexing by the guards, who wanted to show Britain and America that their presence in Iraq was unwelcome; the latest standoff - which provoked a UN Security Council statement on 29 March, calling for an early settlement of the dispute (albeit in weaker terms than Britain had wanted) brings the west into more direct and prolonged conflict with Iran's militant defenders, and signals further their independence and power within the regime.

These moves can be interpreted as internal pressure-tactics to force more pragmatic Iranian strategists into a harder line against the west. In taking western hostages, the guards have taken the Tehran regime itself hostage in an effort to enforce their confrontational ideology and posture. Moreover, in taking advantage of the deep fissures within the Iranian state, the Revolutionary Guards have created a fait accompli, forcing the government to adopt a position from which it will be hard to back down. Pragmatists and reformists - from former president Mohammad Khatami to nuclear negotiator Ali Larijani - continue to push a significantly more moderate line in the face of hardline resilience. The guards however, driven by their experiences of the revolution and eight bloody years of war with Iraq, want to see Iran take a more aggressive stance against Britain and America and preserve Iran's nuclear integrity. This ideological confrontation over the sustainability of Iran's revolutionary principles exemplifies the domestic contest at the heart of Iranian politics.

The politics of confrontation

The latest confrontation, broadly reminiscent of the 1979-80 hostage crisis involving Iran and the United States, stems from an internal desire to show Britain and America that Iran has the ability to respond despite coming under sanction for its nuclear programme. Revolutionary guards and their supporters in government have always viewed the occupations in Iraq and Afghanistan with the deepest suspicion and accuse America and Britain of fomenting unrest among their own ethnic minorities. In addition, the Iranian authorities themselves are under mounting pressure domestically to ensure the release of five Iranian officials held by the United States military in Iraq after their detention in Irbil in January 2007, and hardliners are arguing that any release of the British military personnel should be conditional on the release of the Iranians.

For Tehran, a clear advantage of a crisis such as this has provoked market fears and an increase in oil prices to $68 a barrel, thus filling Iran's energy coffers. The government can reward its favoured constituencies, and a hard-pressed people who already suffer from the mismanagement of the Iranian economy and fear the repercussions of sanctions are offered at least the possibility of welcome band-aid.

Iran's bullying tactics and short-term benefits notwithstanding, the regime is more isolated than ever. Yet even under mounting pressure it is unlikely that this regime will look for a quick resolution to this crisis. For now, the distraction provides Tehran cover while it rallies a domestic consensus on the nuclear programme. Moreover, a compromise on this issue will return both domestic and international attention to the next round of negotiation. While such an aggressive strategy is risky for Tehran, the regime will take the risk of further isolation to seek to bolster regional support and fortify at home.

The weakness and insecurity evident in Iran's leadership is dangerous, for they both project and sanction irrational behaviour. But there is a political logic at work. The Tehran regime's hardline elements continue such activities in order to consolidate their influence and perpetuate Iran's political system. The international community has no choice but to remain vigilant in its attempts to tame Iran's nuclear and regional ambitions.