Tedros Adhanom Ghebreyesus warned that the impact of the conflict, sparked by the US-Israeli attacks on Iran on Saturday, "goes beyond the immediately affected countries".

"Operations at WHO's logistics hub for global health emergencies in Dubai are currently on hold due to insecurity," he told a press conference.

Last year, the Dubai logistics hub processed more than 500 emergency orders for 75 countries around the world, Hanan Balkhy, the WHO's Eastern Mediterranean regional director, told reporters.

"Humanitarian health supply chains are now being jeopardised," she warned.

Balkhy explained that "the hub's operations are temporarily on hold due to insecurity, airspace closures and restrictions affecting access to the Strait of Hormuz".

The disruption, she said, was "preventing access to $18 million in humanitarian health supplies while another $8 million in shipments cannot reach the hub".

It was affecting more than 50 emergency supply requests from 25 countries, as well as some $6 million in medicines destined for the war-torn Gaza Strip.

- 'Extremely important lifeline' -

On top of that, $1.6 million in polio laboratory supplies were being held up, which could have dire impacts for Afghanistan and Pakistan, where the disease is endemic, she cautioned.

Balkhy said the WHO was discussing and coordinating with authorities in the United Arab Emirates on how to continue using the hub.

It was also in discussions with other countries and humanitarian partners on using other hubs in Nairobi, Dakar and Brindisi to establish other routes.

If the conflict draws out, Balkhy acknowledged there could be a need to discuss "all types of potential road routes or ground routes, potentially through the Kingdom of Saudi Arabia", but said the WHO hoped it would not need to do so.

"The Dubai hub is an extremely important lifeline for the humanitarian response," she said.

- 'Nuclear risks' -

As for the direct impact of war, Balkhy said the UN health agency was coordinating the health response across 16 affected countries, and was supporting health ministries and partners "to sustain essential services".

The WHO was also "strengthening disease surveillance and preparing for potential mass casualties and displacement", she said.

Iran meanwhile had not made any "formal request for any specific supplies" from WHO, "as their system is withholding and withstanding the current situation", Balkhy said.

But she said the WHO was "scaling readiness for chemical, biological, radiological and nuclear risks".

Tedros also pointed to the threats to nuclear facilities posed by the conflict.

"Any compromise to nuclear safety could have serious public health consequences," he warned.

The WHO also sounded the alarm over the more than a dozen attacks on healthcare registered by Thursday in the not even one-week-old conflict.

The organisation said it had so far verified 13 attacks on healthcare in Iran, killing four people and injuring 25, while an attack in Lebanon killed three paramedics and injured six others.

"Under international humanitarian law, health care must be protected and not attacked," Tedros said.