To some, Iran's response since US and Israeli strikes killed supreme leader Ali Khamenei on the war's first day look like those of a decapitated and directionless power.

Why is Iran targeting Gulf countries, Turkey and Azerbaijan with air strikes? Why not seek those countries' support, or at least keep them neutral?

But various analysts see a well-honed strategy of asymmetric warfare in Iran's retaliatory offensive: resist the onslaught, and make the enemy pay a price so heavy they have to give up.

"Iran's strategy is to create pressure on Washington, DC by angering the Gulf and by creating upward trends in the price of oil, gas and other commodities," said Burcu Ozcelik, a Middle East security expert at Britain's Royal United Services Institute.

Although Iran's leadership was badly shaken by the strikes that killed Khamenei -- now replaced by his son Mojtaba as supreme leader -- and other top figures, the system is holding so far.

And the Islamic Republic is digging in for an all-or-nothing fight, against a United States that has less at stake.

- 'Exit ramp' -

Tehran has little chance of defeating the US military.

But it can hope to outlast the current campaign, which is limited to air strikes. US President Donald Trump will meanwhile have to think hard about the potential political costs before sending in ground troops.

"Tehran is trying to raise the cost of escalation until Washington starts looking for an exit ramp," said Ali Vaez, an Iran expert at the International Crisis Group.

It is a page straight out of the textbook on asymmetric warfare.

In a classic 1975 paper, "Why Big Nations Lose Small Wars", the late professor Andrew Mack unpacked the reasons for outcomes such as the US defeat in Vietnam.

He underlined how weaker powers can exploit the gradual diminishing of a stronger adversary's political capacity to wage war.

Since the Iranians "don't have unlimited supplies of missiles and drones, we see them trying to use their firepower carefully, to make the conflict last long enough that Trump eventually says, 'That's enough'", said Agnes Levallois, head of the Middle East-focused think tank iReMMo.

"The longer the conflict lasts, the more Tehran believes the strategic balance -- psychologically and politically -- begins to shift" in its favour, said Danny Citrinowicz, of Israel's Institute for National Security Studies.

And the Iranian toolkit goes deeper.

"Tehran, cognizant of its inability to win a conventional war against the US, relies on irregular tactics to drag out the war, primarily through economic coercion and cost asymmetry," said a briefing by the US research centre Soufan.

That includes sowing chaos in the Middle East, bombing neighbouring countries and sending global oil and gas prices skywards by effectively shutting the crucial Strait of Hormuz.

- War of attrition -

If Trump comes under enough pressure from Gulf allies and energy inflation, he may have to fold.

"Market impacts, Hormuz disruptions and oil prices are all variables that will weigh heavily on Washington's thinking," said analyst Emily Stromquist of US advisory firm Teneo.

The strategy relies on the assumption that Gulf countries will have more pull on Trump than key US ally Israel, which is gunning for regime change in Iran.

If the Islamic Republic survives, it may pay a heavy price.

"The regime in Iran will have to make some deep concessions" in any end-game, said Ozcelik.

The Gulf states "will want to have some influence" in any ceasefire agreement, and Iran's relations with the rest of the region will be badly damaged, she said.

But none of that likely matters to Tehran, said Citrinowicz.

"From Iran's perspective, the goal of this war is to maximize its gains and 'imprint' in the minds of its adversaries the costs of fighting Iran in the future," he said.