The United States and Iran have traded strikes in the first such confrontation since a preliminary agreement was reached on June 15 to end the months-long war.

Both sides traded blame, accusing each other of violating the terms of the memorandum of understanding (MoU) signed by US President Donald Trump and his Iranian counterpart, Masoud Pezeshkian.

At the heart of the latest escalation lies a struggle for control of the Strait of Hormuz, which was blocked by Iran in response to the US-Israeli war. Tehran has used the waterway – a global energy chokepoint – as a geostrategic leverage point.

So, what’s behind the US strikes on Iranian territory and where has Tehran returned fire? Will it unravel the agreement between the two sides?

Where has the US struck and why?

The US Central Command said that the military’s aircraft struck missile and drone storage locations and radar sites along Iran’s southern coastline late on Friday, “as a powerful response to yesterday’s attack on a commercial ship that was transiting the Strait of Hormuz”.

On Thursday, a Singapore-flagged commercial vessel, Ever Lovely, was struck by an unknown projectile off Oman’s coast. Iran did not acknowledge the attack, but did not deny it either.

President Trump had called the attack “a foolish violation” of the ceasefire agreement, adding that US forces also intercepted three other drones launched in the same coordinated attack.

Later, the US military published a grainy black-and-white video of an explosion labelled “unclassified,” noting that “the unwarranted aggression against commercial shipping by Iranian forces clearly violated the ceasefire”.

“Iran’s dangerous behavior undermined freedom of navigation as commerce increasingly flows through the vital international trade corridor,” the US military added, referring to the uptick in traffic in the Strait of Hormuz since the agreement was reached.

It added that the US would continue to provide “safe passage coordination and support” to commercial vessels transiting the strait.

Iran said a projectile struck the area around a pier in Sirik in southern Hormozgan province.

Iran’s Mehr news agency quoted the head of ports at eastern Hormozgan, who said that no damage has been caused to the Sirik port – and that it was operating normally with no damage to its equipment.

Where has Iran struck and why?

Iran’s Islamic Revolutionary Guard Corps (IRGC) said it responded with attacks against US military installations in the region. Tehran did not provide details about what may have been hit.

In a statement to the government news service IRNA, the IRGC warned, “In the event of repeated aggression, our response will be more extensive than this.”

On Saturday, Bahrain’s Foreign Ministry condemned “an alleged Iranian drone attack on its territory”, describing it as a serious violation of sovereignty and international law. It said the incident endangered civilians and undermined regional de-escalation efforts, placing responsibility on Tehran for escalating tensions.

A tanker was hit by an unidentified projectile, the United Kingdom Maritime Trade Operations (UKMTO) said on Saturday, adding that all crew are reported safe.

Late on Thursday, the IRGC warned against an alternative route in the waterway. Only routes approved by Tehran could ensure safe passage through the strategic waterway, it said.

The warning came after Oman had announced a new route in the southern section of the strait, closer to the Omani coast.

The Iranian foreign ministry condemned the latest US attacks, saying the targeting of “coastal surveillance facilities violate Article 1 of the Memorandum of Understanding,” which mandates the end of hostilities on all fronts. Tehran said the US attack was also a violation of the UN Charter.

Who controls the Strait of Hormuz?

Iran says it maintains the control – and the right of management – over the waterway, which has come to be Tehran’s biggest bargaining chip in negotiations with the US and Israel.

Iran’s de facto blockade of the strait triggered a global energy crisis. Higher fuel prices in the US caused by the war have piled political pressure on Trump to end it.

Tehran has been aiming to impose tolls or fees on ships passing through the waterway. Its leaders have asserted that the strait will never return to its pre-war status. The US and Gulf countries have rejected the idea of paying Iran for transit.

Iran first published its own map of approved navigation routes in April, directing ships to sail much closer to the Iranian coastline than before the conflict, and also set up a body to manage the strait.

Kazem Gharibabadi, Iran’s deputy foreign minister, said that “any credible framework must be based on coordination with Iran and the provisions of paragraph five of the Islamabad Memorandum of Understanding”.

As per that MoU, Iran agreed to “make arrangements using its best efforts for the safe passage of commercial vessels with no charge, for 60 days only, from the Persian Gulf to the Sea of Oman and vice versa”.

It also provides for discussions between Iran, Oman and other Gulf states over future arrangements for managing navigation through the waterway “in line with the applicable international law and the sovereign rights of coastal states of the Strait of Hormuz”.

The agreement does not specify what will happen after the initial 60-day period.

On Wednesday, US Secretary of State Marco Rubio said Iran will not be permitted to charge tolls or fees for vessels transiting the waterway.

The two sides have set 60 days to agree on a final deal.

Al Jazeera’s Resul Serdar Atas, reporting from Tehran, said that the recent escalation is the main threat to the ongoing negotiations.

“The reason why Iranians are insisting on this [control over Hormuz] is because the Strait of Hormuz is the biggest leverage that Iranians have. They believe that if they lose that pressure tool, their hand is going to be significantly weakened at the negotiating table,” he said.

Is the MoU unravelling?

Trita Parsi, executive vice president of the Quincy Institute for Responsible Statecraft, told Al Jazeera that the latest strikes are “definitely putting the MoU under immense stress”.

“On the one hand, the US and Iran may continue shooting at each other in the Strait of Hormuz,” he said. “On the other hand, the Israeli-Lebanese agreement appears to contradict the MoU by allowing Israel to continue to occupy parts of Lebanon.

“Put together, the odds against the MoU rise sharply,” he said.

Last Monday, after the first round of talks ended in Switzerland, mediators said that Washington and Tehran had agreed to set up new communication lines to ensure the Strait of Hormuz is open and end fighting in Lebanon.

But that did not prevent the latest military confrontations. “If they have disagreements about how the MoU is being applied, they can pick up the phone. But violence will be met with violence,” US Vice President JD Vance said on X.

Andrea Dessi of the American University of Rome believes the recent escalation shows that “the MoU is extremely delicate and has the possibility of collapsing at any moment”.

“Clearly, it is in the interest of both sides, Iran and the United States, not to let this escalate into a further all-out conflict,” he said.

“Both sides have a specific interest in demonstrating that their ability to control or command the strait is in their hands,” the analyst said.

“Therefore, this is setting up something of a tension and a potential clash which could spiral out of control at any moment.”