The Middle East is in the grip of an “unprecedented” catastrophe that could “spin out of control”, the World Health Organisation has warned, as the US, Iran and Israel unleash their heaviest exchange of fire since the war erupted.

Donald Trump has repeatedly signalled that the US’s bombing campaign of Iran may end soon, telling Axios on Wednesday there was “practically nothing left” to target.

But together with Israel, the US continued to pound Iran, including oil facilities, sending fiery toxic clouds above Tehran in what the US defence secretary Pete Hegseth called “our most intense day of strikes”.

Iran, meanwhile, fired missiles and drones at targets across Israel and the Gulf, including a US base in Kuwait, while Israel pounded suburbs and central Beirut through the night. Lebanon said at least seven people were killed in heavy strikes on the city’s Corniche, a seaside promenade where displaced families had been sleeping rough.

Dr Hanan Balkhy, director of the UN health agency, warned of an “unprecedented, long lasting impact” on the region if the hostilities continue to escalate, adding that the WHO was preparing “for chemical, radiological, nuclear and biological risks”.

She said the WHO had received multiple reports of oil-laden “black rain” this week in Iran, after Tehran was choked in black smoke on Monday when an oil refinery was hit.

“It’s unprecedented. This is a multi-country, multi-region escalation that is taking place,” she told The Independent.

“It can spin out of control and lead to even more damage through a chemical, nuclear or radiological war, which will have an unprecedented, long lasting impact on the environment and on people that will go beyond the countries involved.

“We really need to call upon everyone to go back to diplomacy, negotiations and discussions, and to refrain from war and from attacks, whether on health care or on the environment.”

Trump has repeatedly tried to reassure markets this week that the US campaign on Iran, which triggered the region-wide conflict, will end soon. He told Axios there was only a “little this and that” left to hit in Iran, adding: “Any time I want it to end, it will end.”

The US-Israeli war on Iran and Tehran’s attacks on Gulf neighbours has not only seen mass displacement, death and destruction, but impacted the global economy as Iran has choked shipments via the world’s most important oil artery, the Strait of Hormuz.

There are now concerns about environmental devastation. In Iran, citizens reported “black rain” and shared images of fiery clouds dominating the skies above the capital amid US and Israeli strikes on oil facilities.

In Lebanon, Israel continued its offensive against Iran-backed Lebanese militant group Hezbollah for a 10th day after it had fired on Israel in response to Israel’s killing of Iran’s Supreme Leader.

Israel has put swathes of Lebanon under evacuation orders, forcing five hospitals to close, the country’s health minister told The Independent, adding that health system was struggling as now more than 800,000 people have been displaced and over 600 killed, according to the latest count.

The country was already reeling from the aftermath of the 2024 war with Israel, and an unprecedented financial collapse five years ago.

“We need specific medication, like surgical kits and first aid kits, from the international community,” said minister Rakan Nassereddine from a school in central Beirut which had been turned into a camp for those displaced from the south.

“The main call is to stop attacking civilians and to stop attacking the medical services, medical sector and ambulances,” he added.

Israel launched a fresh wave of strikes against the southern suburb of Beirut, and struck a residential district in the west of the city overnight.

At that site, Faysal, 55, a father of two, described being thrown from his bed when an Israeli strike blasted out the side of the building opposite him at dawn.

Just days before, Faysal had fled his village in the war-ravaged south to what he thought was the comparative safety of this neighbourhood in Beirut.

“We saw everything on the ground here collapse,” he said, standing on a street strewn with destroyed chunks of building glass, and crushed cars.

“Everyone was running, people carrying their children and running through the destroyed streets. It was a terrifying sight. There are no safe areas any more.”

Veteran British-Palestinian plastic surgeon Ghassan Abu Sittah, who worked in Gaza and is currently in Lebanon treating some of the most gravely wounded children, said there was not even a “glimmer of hope” that Israel’s offensive was abating.

“It is really at the very beginning,” he continued, adding that Lebanon was not able to cope.

“My fear is that the Israelis will do what they were doing in Gaza, and what they did in the previous war, which is start to take out one hospital after another to increase the pressure by reducing the capacity of the health system.”

Abu Sittah said the issue was compounded by the fact that countries in the region which had stepped in before were now unable to do so as they were also under fire.

“In the previous war the Qatari Red Crescent Society stepped in. The Kuwaiti Red Crescent Society stepped in. Now everybody is involved in their own problems, and we are at a point where you rarely hear of anything coming in.”