Iran has rejected a U.S. ultimatum to reopen the Strait of Hormuz by a deadline set by former U.S. President Donald Trump, as military strikes intensified and diplomatic efforts led by Pakistan approached what officials described as a critical stage.

With hours remaining before the deadline, a senior Iranian source said Tehran would not reopen the strategic waterway without concessions from Washington that had not been offered. The Strait of Hormuz, a key global energy corridor, has effectively been closed by Iran to most international shipping since late February following joint U.S.-Israeli military actions.

Trump warned that failure to comply would result in large-scale destruction of Iranian infrastructure, including power grids and bridges. In a social media post, he stated that “a whole civilization will die tonight,” framing the moment as a pivotal point in global history.

The remarks drew criticism from legal experts, including a former U.S. State Department adviser now with the International Crisis Group, who said the language could be interpreted as a threat violating international norms.

Military activity escalated across Iran throughout the day. Strikes were reported on transport infrastructure, including railway and highway bridges, as well as an airport and a petrochemical facility. U.S. forces also targeted installations on Kharg Island, which hosts Iran’s primary oil export terminal.

Power outages were reported in parts of Karaj following damage to transmission lines and a substation.Iran signalled a broadening of its response. Officials warned that Gulf states aligned with Washington could face retaliatory strikes on critical infrastructure.

A senior Iranian source said such actions could disrupt electricity and water supplies in desert cities dependent on energy systems.Iran’s Revolutionary Guards issued a statement saying previous restraint had ended and that Tehran would seek to deprive the United States and its regional allies of oil and gas resources.

Iranian authorities also claimed responsibility for attacks on a vessel in the Gulf and on a major Saudi petrochemical facility in Jubail, where international energy companies operate.In parallel, reports emerged of an overnight strike on a synagogue in Tehran, which Iranian officials attributed to Israeli forces.

Footage aired by state media showed debris scattered across the site, including religious texts. Israel’s military did not immediately comment on the incident.Diplomatic efforts led by Pakistan continued amid the escalation.

Iranian officials said mediation attempts were “approaching a critical, sensitive stage,” with Islamabad relaying messages between the two sides. A proposal under discussion included a temporary ceasefire and partial reopening of the strait, with broader negotiations to follow.

However, Iranian sources said Tehran had rejected interim arrangements, insisting instead on a permanent cessation of hostilities, guarantees against future attacks and compensation for damage.Iran’s conditions, as outlined through official channels, also included maintaining control over the strait and introducing a mechanism to regulate transit, potentially involving fees.

Prior to the conflict, the waterway functioned as an open international route through which roughly one-fifth of global oil and liquefied natural gas supplies passed.Despite the intensifying conflict, global markets showed limited reaction, reflecting uncertainty over whether the U.S. would carry out the threatened escalation.

Trump has previously issued similar warnings but later stepped back, citing unspecified progress in talks, claims that Iranian officials have denied.On the ground, residents expressed concern over the prospect of further escalation.

A resident in Isfahan said she hoped the latest threats would not materialise, reflecting broader public anxiety as military actions continued.Iran maintains that any negotiations must follow a halt to U.S. and Israeli strikes and include the lifting of sanctions.

Without such measures, officials indicated that Tehran would continue its current posture, including restrictions on maritime transit through the Strait of Hormuz.

As the deadline approached, neither side signalled a willingness to compromise, raising the risk of further escalation in a conflict that has already disrupted regional stability and global energy flows.