Proposals for an immediate ceasefire have been circulated to Washington and Tehran in an attempt to halt the five-week-old war and stave off an extraordinary threat issued by Donald Trump to bomb Iran’s power plants.

Mediators from Pakistan, Egypt and Turkey want both sides to agree to suspend hostilities and reopen the strait of Hormuz, to be followed by a period of detailed negotiations intended to reach a more complete peace agreement.

Trump demanded on Sunday that Iran “Open the Fuckin’ Strait” by Tuesday evening or else he would target the country’s power plants and bridges.

Iranian officials told Reuters they would not open the strait to merchant shipping as part of a temporary ceasefire. Another report, on the Axios news site, suggested Iran does not want to be caught in a situation where there is an agreement on paper but the US and Israel periodically attack anyway.

Iran’s foreign ministry spokesperson Esmaeil Baghaei said Tehran had responded privately, but added that peace negotiations were “incompatible with ultimatums and threats to commit war crimes”. The country’s central military command warned of a “much more devastating” retaliation should the US and Israel escalate.

Bombing power plants and bridges has been condemned by lawyers and experts as a likely war crime because its impact on civilians would be disproportionate to whatever notional military advantage is gained.

Ceasefire discussions have involved Pakistan’s army chief, Field Marshal Asim Munir, in contact with the US vice-president, JD Vance, while Trump’s special envoy Steve Witkoff has been in contact with Iran’s foreign minister, Abbas Araghchi.

Israeli political sources told the country’s Haaretz newspaper that they believed the talks were likely to collapse, though they thought Trump was looking for a way to end the war. Israel was preparing for all scenarios, they added, and had identified further targets if the bombing of energy and infrastructure targets goes ahead.

Israel has already shown its willingness to step up its bombing. Iranian news agencies reported explosions at Iran’s South Pars petrochemical complex in Asaluyeh. Israel claimed responsibility shortly afterwards through its defence minister, Israel Katz.

The minister said the IDF had struck “the largest petrochemical facility in Iran” and that the attack had come after a separate strike on the Mahshahr complex on Saturday. Katz said the two sites were “responsible for roughly 85% of Iran’s petrochemical exports and have now been put out of operation”.

Oil prices dipped on Monday morning, reflecting hopes for a de-escalation. Brent crude futures fell by $1.92, or 1.76%, to $107.11 a barrel by mid-morning before ticking back up above $108 as the fighting continued. Prices were at $70 a barrel before the US and Israel attacked Iran at the end February.

Israel’s military said it had bombed Tehran again on Monday and that another strike on Sunday killed Majid Khademi, the head of intelligence of Iran’s Revolutionary Guards.

Four people were confirmed dead in Haifa, northern Israel, on Monday after a missile strike the day before, as a rescue team recovered all the bodies buried beneath the rubble. The missile got through Isreal’s air defences and destroyed a building.

Israel bombed Beirut’s southern suburbs on Monday, where Hezbollah has its stronghold in the capital. A day earlier, 15 people were killed in Lebanon, including Pierre Mouawad, an official in the anti-Hezbollah Christian party, who was one of three people who died in a strike on Ain Saadeh, east of Beirut.