The sudden eruption of fresh hostilities in the Gulf – just 10 days after Iran and the US signed a memorandum of understanding to end the conflict – threatens to put the two countries back on the path to war.

It appears the deliberately opaque wording in the memorandum has been unable to withstand the pressure of conflicting interpretations, and as a result supporters of the deal inside Tehran are on the back foot. Statements to the effect that Iran’s government should never have agreed to reopen the strait of Hormuz are proliferating – and not just among the country’s hardliners.

The wording of the 14-point document was deliberately broad on two of the most vexed issues, the Lebanon ceasefire and the strait, in the hope that as trust developed between the two sides, a modus vivendi could be found. Instead, the agreement is crumbling under the pressure, with each side accusing the other of violating its terms.

In Lebanon, the difficulty is that two ceasefire agreements had been agreed – and they are pulling against each other.

The first ceasefire, mentioned in the memorandum and developed at the Lucerne talks attended by the US vice-president, JD Vance, gave a new role in Lebanon for Iran, and hence its proxy Hezbollah. Iran was to join a new deconfliction mechanism, and it seemed as if Israel was being squeezed out.

The second, fuller, ceasefire signed by the Israel and Lebanese government in Washington on Friday and overseen by the US secretary of state, Marco Rubio, reverses all that, by excluding Iran and Hezbollah. It allowed for Israel to remain in southern Lebanon until the complete disarmament of Hezbollah – a condition the Shia force could never accept.

The agreement – signed by Nawaf Salam, the Lebanese prime minister and a former head of the international court of justice – also contained a clause stating that both sides would cease all hostile actions in all legal fora, leaving Israel immune from prosecution for any alleged war crimes committed in Lebanon.

The Israeli prime minister, Benjamin Netanyahu, responded to that deal triumphantly, saying: “We will stay in the area until Hezbollah’s weapons and those of the remaining terrorist groups are dismantled.”

But it is very hard to see how the ceasefire signed by the Lebanese government could ever be remotely acceptable to Hezbollah or Iran. The agreement is framed as reinforcing Lebanese sovereignty – but makes that sovereignty entirely conditional.

The memorandum of understanding has also proved equally ineffective in opening the strait of Hormuz.

The document states that Iran will “make arrangements using its best efforts for the safe passage of commercial vessels” through the strait with no charge for 60 days. It left “arrangements” and “best efforts” undefined, and made no reference to any other action to clear the strait, leaving the impression that Iran was the dominant actor.

For the future, the memorandum said, Iran would hold a dialogue to define the future administration and maritime services in the strait, “in discussion with other Persian Gulf littoral states in line with the applicable international law and the sovereign rights of coastal states of the Strait of Hormuz”.

Although it could seem that Iran had interpreted that language to mean that it alone can determine which route ships must take, Tehran had last week been working with the UN’s International Maritime Organization and Oman on an evacuation plan to allow hundreds of ships through the strait.

The IMO secretary general, Arsenio Domínguez, felt he had Iran’s agreement to launch that plan, offering a northern and southern route throught the strait. Yet on Thursday morning the Islamic Revolutionary Guards Corps Navy said ships could only use the northern route to exit the strait and in the afternoon, the Ever Lovely, a Singapore-flagged, 2015-built Evergreen container ship, was struck while transiting a southern route close to Oman.

Domíngues halted his scheme, saying the IMO would not put seafarers at risk, but despite Thursday’s attack, ships have continued to venture through the strait.

Behind that incident may be an Iranian fear that the southern route, along the coast of Oman, will give the US a way to end the Iranian chokehold. Behind that is a further Oman-Iran discussion about a long-term solution for management of the strait that Iran might yet accept.

Oman will want to frame any proposals in the context of Unclos, the UN convention on the law of the sea, and so will rule out tolls. But Article 41 of Unclos allows strait states to designate sea lanes and set up traffic separation schemes. Article 43 would allow for Oman in consultation with the IMO to ask stakeholders with a shared interest in navigational aids in the strait to contribute to a funded “cooperative mechanism” to help with these maritime services. In theory, charges could be levied by Oman for specific navigational safety services if they conferred a direct benefit on a ship, but there could be no general levy.

For now, however, as the bombing recommences, creative legal ideas appear to have been put to one side as the men of war return to centre stage.