Clashing interpretations of vague memorandum of understanding language on Hormuz at heart of escalation, analysts say.
When Iran faced an all-out war against the United States and Israel, Tehran did not respond with missiles and drones alone; it shut down the Strait of Hormuz, a vital waterway for global energy.
As Iran and the US moved towards a ceasefire, Iran saw control of the Strait of Hormuz as a strategic gain it was unwilling to relinquish.
But Washington wanted the waterway to return to its pre-war status as a free-for-all international shipping lane.
That fundamental disagreement over the strait is at the core of the renewed clashes between the two countries, analysts say.
The ongoing skirmishes started on Monday after at least three suspected Iranian attacks on commercial ships sailing outside the route designated by the Islamic Revolutionary Guard Corps (IRGC).
The US responded with waves of strikes against dozens of targets on the southern shores of Iran. In turn, Iran retaliated with missile and drone attacks against US bases across the region.
US President Donald Trump declared on Wednesday that the memorandum of understanding (MoU) that established the truce and negotiations process between the two countries was “over”. More fighting followed on Thursday.
“The MoU committed both sides to keeping the Strait open through coordinated arrangements for safe commercial navigation, not unilateral action,” Negar Mortazavi, a senior fellow at the Center for International Policy.
“From Tehran’s perspective, that means any passage or maritime security arrangements should be coordinated with Iran.”
Some ships have been hugging the Omani coast and passing through the strait without coordinating with Iran, a move that Mortazavi says establishes “parallel shipping routes and security mechanisms” in the strait without Tehran.
“Iran sees that as a direct violation of the MoU, and that’s why Hormuz has become the first major test of how the agreement will be interpreted and enforced,” she told Al Jazeera.
The text of the deal is not definitive when it comes to Hormuz. While it tasks Iran with de-mining and ensuring safe navigation in the strait, it says ships must pass free of charge for the first 60 days of the MoU.
The time period does not rule out that Iran may set up a toll system as part of a final agreement.
At the same time, the memorandum says that Iran would hold discussions with Oman and Gulf countries to “define the future administration and maritime services” in the waterway “in line with applicable international law and the sovereign rights of coastal states of the Strait of Hormuz”.
The conflicting interpretations by the two sides render parts of the MoU contradictory.
“The text of the memorandum itself doesn’t exactly say much about how things are going to look during the implementation of the agreement,” said Ryan Costello, the policy director at the National Iranian American Council (NIAC).
“Iran interprets it as Iran controlling who goes where, whereas the US has sought to undermine that and set up essentially a second transit route through the Strait.”
The US military’s CENTCOM in the Middle East shared a social media post on Thursday, presented as a fact check, denying that passage through Hormuz is permitted only via routes designated by Iran.
“TRUTH: Iran does not control the Strait of Hormuz. Since early May, US forces have helped facilitate the successful transit of more than 800 commercial vessels and 380 million barrels of crude oil through the vital international trade corridor,” CENTCOM said.
For Iran, oversight on Hormuz is essential, experts say, not just because of the potential fees that could run in the tens of billions of dollars annually, but as a means of deterrence against future attacks by the US and Israel.
In his first statement as supreme leader after succeeding his slain father in March, Mojtaba Khamenei underscored the importance of control over the waterway.
“The lever of closing the Strait of Hormuz must certainly continue to be used,” he wrote.
Costello said there is a perception in Iran that power over Hormuz is a vital asset.
“There is a sense that the US is seeking to undermine a new strategic advantage for Iran and one that may be even more significant, at least in the near and medium term, to Iran’s leverage than even its nuclear programme had been,” he told Al Jazeera.
“And so, if the US is effectively able to undermine Iran’s control of the strait, then that could reduce Iran’s leverage overall and deterrence to prevent another resumption of the war.”
The closure of the waterway after the initial US and Israeli strikes on February 28 sent global oil prices soaring. Petrol in the US reached more than $4.5 per gallon (3.78 litres), up from less than $3 before the war, which fuelled inflation and public discontent with the conflict.
Trump has openly suggested if it were not for US public pressure, he would prolong the war with Iran and take the country’s oil. The US president said in April that it was “unfortunate” that Americans do not have the “patience” for a drawn-out conflict with Tehran.
When the fighting appeared to end with the 14-point memorandum in mid-June, the markets took a proverbial sigh of relief.
The US lifted its naval blockade on Iran, Hormuz was reopened, stocks rose and oil prices began to drop.
However, tensions started to intensify again from the early days of the deal.
The immediate sticking point was Israel’s refusal to stop its attacks and end its occupation of south Lebanon despite the MoU’s explicit call for a region-wide ceasefire and for preserving “the territorial integrity and sovereignty” of the country.
While this week’s clashes have been the most severe, it is not the first time the truce has been challenged.
The first outburst of violence after the MoU was over Hormuz.
A Singapore-flagged commercial vessel was attacked off the coast of Oman on June 25. The US then launched strikes on southern Iran, and the Iranian military responded with missile attacks against bases hosting American troops in Gulf countries.
That episode remained limited and concluded quickly. But the current cycle is more intense and appears to be escalating.
Earlier this week, the US also revoked sanctions waivers on Iranian oil granted as part of the ceasefire deal.
Despite the outbreak of violence, both sides have domestic realities that may dissuade them from a return to an all-out war, Costello said.
In Iran, inflation is out of control, and the economy is reeling from decades of sanctions while the government continues to face the risk of anti-government protests akin to the demonstrations that swept the country in January.
On the American side, oil reserves that created a buffer to tame skyrocketing petrol prices during the war are running low. And the midterm elections that will decide control of Congress are set to take place in November, less than four months away.
“There are strategic reasons why one can hope that this war does not last much longer than it already has,” Costello told Al Jazeera.
He added that Trump opened up a Pandora’s box by launching the conflict, which has proven to be much more difficult to end than to start and risks turning into another “forever war” in the Middle East.
For her part, Mortazavi said the MoU was supposed to stop the war, but it did not resolve the underlying disputes between Washington and Tehran.
“This was a framework for managing conflict, not a comprehensive peace agreement. Both sides are now testing its limits and trying to establish their own interpretation of what was signed,” she told Al Jazeera.
“What we’re seeing is a struggle over implementation as much as a return to confrontation.”
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