The sound of a large explosion reverberated around the Ukrainian port of Odesa as President Volodymyr Zelenskyy and Greece’s prime minister ended a tour of the war-ravaged southern city Wednesday.

Greek Prime Minister Kyriakos Mitsotakis said the delegations were getting into their vehicles when they heard the blast, which he called a “vivid reminder” that Odesa is gripped by the war with Russia. It is one thing to hear about the war and “quite another to experience war firsthand,” Mitsotakis said.

Zelenskyy said the explosion caused an unknown number of dead and wounded. “You see who we’re dealing with, they don’t care where to hit,” he told reporters.

Russian officials made no immediate comment.

Zelenskyy has regularly visited cities and military units on the front line during the war, always in secrecy until after he has left. Foreign leaders have made numerous trips to Ukraine, and they occasionally have had to take refuge in shelters when air raid sirens sound.

European Commission President Ursula von der Leyen condemned on X, formerly Twitter, what she called the “vile attack” during the Greek visit. She called it a “new attempt at terror” by Russia.

Zelenskyy showed Mitsotakis around the destruction in Odesa, where in the most recent major Russian attack 12 people — including five children — were killed when debris from a Russian drone hit an apartment block on March 2.

Mitsotakis said Odesa held a special place in Greek history as the place where the Filiki Etairia organization was founded that fought for Greek independence from Ottoman rule in the 19th century.