Iran showed no sign of accepting US President Donald Trump's ultimatum to open the Strait of Hormuz by the end of Tuesday, and Trump said "a whole civilization will die tonight" unless Tehran reached ​a last-minute deal.

As the clock ticked down on Trump's deadline, strikes on Iran intensified throughout the day, hitting railway and road bridges, an airport and a petrochemical plant and knocking out power lines, according to Iranian ‌media. Explosions were reported on Kharg Island, home to Iran's oil export terminal, which Trump has openly mused about destroying or seizing.

Iran responded by declaring it would no longer hold back from hitting its Gulf neighbors' infrastructure, and claimed to have carried out fresh strikes on a ship in the Gulf and Saudi industrial facilities linked to US firms.

Trump escalated his rhetoric even further. "A whole civilization will die tonight, never to be brought back again. I don't want that to happen, but it probably will," he wrote on his Truth Social website.

"However, now that we have Complete and Total Regime Change, where different, smarter, and less ​radicalized minds prevail, maybe something revolutionarily wonderful can happen, WHO KNOWS? We will find out tonight, one of the most important moments in the long and complex history of the World."

Iran's Islamic Revolutionary Guard Corps (IRGC) warned that if the US army crosses the red line in attacking civilian targets, Iran's response "will go beyond the region."

Israel, in the meantime, warned Iranians to avoid taking trains until 1730 GMT on Tuesday. "Your presence on trains and near railway tracks puts your life in danger," the military wrote on its Persian-language account.

The warning followed reports that Israeli Prime Minister Benjamin Netanyahu had urged Trump not to pursue a ceasefire with Iran at this stage, citing potential risks. Trump, however, said a deal could be reached if Iran meets US demands.

In Budapest, US Vice President JD Vance said Washington remains confident it will still receive a response from Iran before Trump's deadline expires.

Amid the exchange of threats, however, Iranian Ambassador to Pakistan Reza Amiri Moghadam said Islamabad's mediation efforts are approaching a "critical" stage.

Moghadam's remarks came after Iran reportedly rejected a proposal conveyed by intermediaries of a temporary ceasefire.

Talks on a lasting peace could begin only after the US and Israel end their strikes, ⁠provide a guarantee they will not resume and offer compensation for damages, an Iranian source told Reuters, adding that any future settlement must leave Iran in control of the strait, imposing fees on ships that use it.

The Iranian response consisted of 10 clauses, including an end to conflicts in the region, a protocol for safe passage through the Strait of Hormuz, lifting of all sanctions, and reconstruction, the official ​IRNA news agency reported.

Diplomatic efforts led by Pakistan are still under way, Reuters reported, as mediators are facilitating talks between the US and Iran.

"We are in touch with Iranians. They have lately shown flexibility that they could join the talks, but they are at the same time taking hard lines as a prerequisite for any negotiations," a Pakistani security source told Reuters.

He added that Islamabad was persuading Tehran to enter negotiations without prior conditions.

Trump has given Iran until 8 p.m. in ​Washington (midnight GMT and 3:30 a.m. in Tehran) to end its blockade of Gulf oil, saying he will otherwise destroy every bridge and power plant in Iran within four hours. Iran says it will retaliate against infrastructure of US allies in the Gulf, whose ​desert cities would be effectively uninhabitable without power or potable water.

Despite the intensification of strikes on the ground and rhetoric from both sides, global markets were largely frozen, hesitant to bet on whether Trump would follow through on his threats or call them off as he has in the past.

Among the reports of strikes inside Iran throughout the day were attacks on railway bridges, a highway bridge, a petrochemical plant and an airport. Power was knocked out in parts of Karaj just west of Tehran by a strike on transmission lines and a substation.

(With input from agencies)