Katherine Butler: It looks like a victory for Iran – but we've been here before

Is this a positive step towards averting a global crisis or a cynical ploy? For those in Israel and the US who are already convinced Iran is building a nuclear weapon (and enriching uranium to that end) the surprise deal announced yesterday will be seen only as a calculated tactic to divide the world, and thus counter Barack Obama's efforts to force Iran to relinquish its nuclear programme via UN sanctions.

It certainly looks like a victory for Iran. Just as the pace of negotiations on a fourth round of UN sanctions appears to be intensifying in the Security Council, Iran signs up to a fuel exchange deal which appears, at face value, to weaken its capacity to build a bomb (if it had any such intention, at least, which Tehran insists is not the case). We have, of course, been here before. Last October, Iran indicated a willingness to do a similar deal at talks with world powers in Geneva. It was hailed by the White House as a breakthrough. Within weeks it had unravelled.

Even if the latest commitment to ship its low-enriched uranium abroad and out of harm's way is not serious, and only the Iranians know that, the Islamic regime is giving the impression of cooperating. This serves to undercut the diplomatic consensus that Washington had been building around sanctions.

At the very least it buys time by conveying the message that there is still some mileage to be had from negotiation. China, which has a veto in the security council, has always insisted that as long as there is even a scintilla of hope in negotiations, it will hold back from endorsing sanctions. The move will also hurt the internal opposition, which will be dismayed at any sign of international respectability being conferred on the regime.

Critics of the fuel swap will also point out that the deal is worth less than the Geneva one, because back then 1,200kg of enriched uranium represented most of its stockpile. Seven months of enrichment on, the same deal leaves a stockpile of around 800kg on Iranian soil, enough to build a small bomb.

Yet it's still not entirely clear that all the cards are in Iran's hands. Dr Suzanne Maloney, Iran expert at the Saban Centre for Middle East studies at the Brookings Institution, makes the valid point that Iran cannot easily walk away from this deal without massively irking sympathetic countries it has been courting. And while on one level it is a sign the regime is internally stronger than it was last October, when internal criticism from reformists and hardliners alike probably prompted its negotiators to walk away from the table, it also demonstrates the strength of its current desire to avoid economic hardships that might incite another wave of street protests.

And if the deal turns out to be the real thing, President Obama can also claim it is a victory for his administration's diplomacy. Without the pressure of a sanctions threat, he can argue, it would not have been achieved, even if the unlikely midwives had to be Turkey and Brazil.