Kiev said a Russian missile attack killed Spanish citizen Emma Igual and Anthony Ihnat, a Canadian citizen, both of whom worked for the NGO Road to Relief.
Two other volunteers from the group were said to have been injured in the incident in the eastern Donetsk region.
The NGO, which helps evacuate wounded people from frontline areas, said its four volunteers were trapped in the van when it overturned and caught fire after being hit by Russian fire near the town of Chasiv Yar.
A statement on the Instagram page said Mr Ihnat died in the attack, while two others, German medical volunteer Ruben Mawick and Swedish volunteer Johan Mathias Thyr, were seriously injured.
Spain’s acting foreign minister, José Manuel Albares, told Spanish media that officials had received “verbal confirmation” of Ms. Igual’s death.
In his evening speech, Mr. Zelensky paid tribute to the two deceased helpers.
“This Russian shelling confirms once again how close the war against Ukraine is to everyone in the world who truly values human life and sees it as the common moral duty of humanity to stop terror and defeat evil,” said he.
The volunteers were on their way to Bakhmut, the eastern city that was the scene of some of the bloodiest fighting of the war, when they were hit, Road to Relief said.
This came as Russia fired nearly three dozen drones into Kiev early Sunday.
The Ukrainian Air Force said the military destroyed 26 of 33 drones launched by Russia, all targeting Kiev and the surrounding region.
Fragments of downed drones fell on five different districts, Mayor Vitali Klitschko and the city’s military administration said, injuring one person.
The governor of the Kyiv region, Ruslan Kravchenko, wrote on Facebook that the overnight strikes had damaged an unspecified infrastructure facility and eight houses.
Russia initially did not comment on the attacks.
In February, American and medic Pete Reed was killed near Bakhmut when his evacuation vehicle was hit by a missile.
In May, AFP video journalist Arman Soldin was also killed by rocket fire in Khasiv Yar near Bakhmut.
https://www.standard.co.uk/news/world/zelensky-tribute-aid-workers-road-to-relief-killed-ukraine-b1106120.html Volodymyr Zelensky pays tribute to two aid workers killed in a Russian missile attack in eastern Ukraine