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.

The report said any action would likely fall short of a full-scale invasion, instead involving special operations forces and conventional infantry targeting locations such as Kharg Island and coastal areas near the Strait of Hormuz, a critical corridor for global oil shipments.

Washington has already moved thousands of Marines to the Middle East amid the month-long conflict. The first of two contingents arrived on an amphibious assault ship on Friday, according to the U.S. military.

Additional deployments under consideration include forces from the 82nd Airborne Division, alongside approximately 5,000 Marines being repositioned to the region. These reinforcements would add to an estimated 50,000 U.S. troops already stationed across the Middle East, according to media reports.

U.S. Secretary of State Marco Rubio said Washington could achieve its objectives without deploying ground troops but noted that forces were being positioned to give policymakers “maximum” flexibility.

Defense analysts cited in reports said limited operations could aim to secure maritime routes or seize key infrastructure such as Kharg Island, a major hub for Iran’s oil exports.

Military experts have cautioned that even limited ground incursions could lead to prolonged engagement, raising the risk of a broader conflict and increased casualties.

Concerns also persist over the economic implications of instability around the Strait of Hormuz, through which a significant share of global energy supplies passes.

No final decision on ground operations has been announced, and U.S. officials have not publicly confirmed the scope or timing of any potential action.

The report, citing Department of Defense officials, said the proposed deployment could include infantry units and armored assets, reflecting a broader effort to reinforce the U.S. posture in a region already on heightened alert amid the ongoing Iran conflic.

The potential troop increase would add to a growing U.S. presence in the region. The Pentagon is preparing to send at least 1,000 soldiers from the Army’s 82nd Airborne Division, according to earlier reporting by the Associated Press.

This would come alongside approximately 5,000 Marines being repositioned to the Middle East, on top of an existing force of around 50,000 U.S. personnel.The incremental buildup has fueled speculation that Washington is positioning itself for possible limited ground operations tied to strategic objectives linked to Iran’s energy infrastructure and regional waterways.

Analysts say U.S. ground forces could be capable of securing key maritime chokepoints or energy facilities, but warn of the potential for a prolonged and costly engagement. Mick Mulroy, a former deputy assistant secretary of defense, said that while such operations are feasible, the broader question remains whether they are strategically justified.

He noted that diplomacy remains the preferred pathway, though its success depends on both sides demonstrating willingness to compromise.

Trump said on Thursday that Iran had allowed several Pakistan-flagged oil tankers to transit a key maritime route, describing the move as a possible positive signal in the context of ongoing tensions.

The administration continues to balance military preparedness with diplomatic outreach, as indirect contacts between Washington and Tehran raise the prospect of negotiations even as force levels in the region expand.