Airstrikes struck Tehran on Tuesday as Iranian authorities called on civilians, including young people, to form human chains around key infrastructure sites, including power plants, in the hours leading up to a deadline set by U.S. President Donald Trump.

The deadline—8 p.m. in Washington—demands that Iran fully reopen the Strait of Hormuz or face sweeping U.S. strikes targeting critical infrastructure such as power facilities and bridges. While Trump has extended previous deadlines, he signaled this ultimatum could be final, intensifying tensions between Washington and Tehran.

The escalating rhetoric has left many Iranians on edge. Trump warned that failure to comply would result in the destruction of Iran’s energy and transportation infrastructure. In response, Iran’s president said as many as 14 million citizens, including himself, have volunteered to defend the country.

Though Iran lacks the technological and aerial capabilities of U.S. and Israeli forces, its control over the Strait of Hormuz—through which roughly one-fifth of the world’s oil supply passes during peacetime—has had significant economic repercussions globally. The disruption has increased pressure on Washington, both domestically and internationally, to seek a diplomatic resolution.

Officials familiar with ongoing diplomatic efforts said negotiations are continuing. However, Iran has rejected the latest U.S. proposal, and it remains unclear whether an agreement can be reached before the deadline expires. International leaders and legal experts have warned that large-scale strikes of the kind threatened could raise serious concerns under international law, potentially constituting war crimes.

Meanwhile, a new wave of strikes has hit multiple locations across Iran, including residential areas in Tehran, resulting in nearly three dozen fatalities. Iran has retaliated with strikes targeting Israel and Saudi Arabia, prompting the temporary closure of a major bridge in the region.