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Media captionIranian TV footage shows a burning tanker

In the hours after two apparent attacks on tankers in the Gulf of Oman on Thursday, the US military released video footage which it said proved Iran was behind them.

The footage was said to show Iranian special forces removing a mine which had failed to explode.

The footage, though far from conclusive, was certainly more compelling than earlier US assertions of Iranian complicity in attacks in the region, which had not been accompanied by evidence.

But a key question remains – what would be Iran’s motive in attacking a Japanese and a Norwegian tanker carrying petrochemicals from Saudi Arabia and the United Arab Emirates to Singapore and Taiwan?

Iran has come under massive economic pressure over the past year, since US President Donald Trump unilaterally withdrew from the 2015 nuclear deal and re-imposed some of the most aggressive sanctions in US foreign policy history – targeting Iran’s oil sales, wider energy industry, shipping, banking, insurance and more.

The sanctions are designed to dissuade other nations from purchasing Iranian oil, which brings in a huge proportion of Iran’s revenue.

And they are working – Iran’s oil exports are down by more than a third.

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Media captionFootage released by the US military’s Central Command

So far, Iran has in response pursued a policy of strategic patience. But if it was behind Thursday’s attacks, what we may be seeing is the end of that policy.

The strategic patience may have run out.

Iran clearly changed tack last month after the US suspended sanctions waivers which had allowed certain countries to buy oil from Iran – significantly accelerating the Trump administration’s goal of driving down Iran’s exports to zero.

Iran’s response was to scale back its commitments under the nuclear deal and to announce that, if Iran could not export its oil, no other country would be allowed to export theirs.

About 30% of the world’s seaborne oil transports travel through the Strait of Hormuz, a strategic sea passage in the Gulf, on Iran’s south coast.

Iran has made threats in relation to the strait before – but never provably acted on them.

Even back in 2012, when the EU imposed an oil embargo against Tehran as part of a broader sanction regime adopted against the country because of the nuclear impasse, Tehran refrained from closing the passage.

But the re-imposition of sanctions recently by the US has significantly ratcheted up the pressure on Iran, pressure that would go some way to explaining why it might seek to threaten the international oil trade, while its own oil sits bounded by its borders.

The risk of such a strategic move is significant – the fallout is potential military escalation with the US and its allies in the region.

It is not a gamble that would have been made quickly or lightly.

It would have been taken by consensus by all the main heads of the different Iranian political institutions, with Iran’s Islamic Revolution Guards (IRGC) playing a significant part given their influence over all regional dossiers, and the supreme leader, Ayatollah Khamenei, having the final say over all matters of security and international affairs.

If Iran is indeed behind these attacks, it would demonstrate that the country’s key decision makers feel the risk of military escalation is one worth taking.

Iran may suspect that the risk is lower than it first seems, because Mr Trump does not want a war.

Recent statements by the US president suggested that despite his bellicosity, he is open for talks with Iran without pre-conditions.

The Iranians will also be mindful however that Mr Trump’s National Security Adviser John Bolton, a long-time critic of Iran, has openly called for the US to confront Iran.

If strategic patience is in fact at an end, Iran may feel that only by displaying the range and scale of its potential destabilising activities – including disruption of the international oil trade it has been barred from – can it increase its leverage with the US, and pull itself out from under the punishing sanctions its old foe has imposed.

Dr Aniseh Bassiri Tabrizi is a Research Fellow, Middle East Security, at the Royal United Services Institute for Defence and Security Studies