A deadly Russian missile strike on the port city of Odesa appeared to land near Ukraine’s president, Volodymyr Zelenskiy, and the visiting Greek prime minister, Kyriakos Mitsotakis, who described the moment of the bombardment as “intense”.

The attack on port infrastructure on Wednesday killed five people and left an unspecified number of wounded, according to Ukraine’s navy.

“We heard the sound of sirens and explosions that took place near us,” said Mitsotakis, who was holding talks with Zelenskiy. “We did not have time to get to a shelter. It is a very intense experience,” Mitsotakis added in Odesa.

Ukraine stepped up its own attacks behind Russian lines with the apparent killing of a Russian election official on Wednesday with a car bomb and a drone assault on a metal plant.

Russia and Ukraine have increased aerial attacks as Moscow’s troops advance on the frontlines and Kyiv faces a shortage of manpower and weapons.

Ukrainian navy spokesperson Dmytro Pletenchuk confirmed that the Odesa strike came as the Greek delegation was visiting the port with Zelenskiy.

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Russian forces “don’t care whether [targets] are military or civilians; whoever they are, whether they are international guests, these people don’t care”, Zelenskiy said.

A White House spokesperson in Washington said: “It appears that [the rocket] landed near the convoy.”

But the Russian defence ministry claimed that the strike was on a “hangar in a commercial port area of Odesa in which crewless cutters were being prepared for combat use by the Ukrainian armed forces”.

Mitsotakis later emphasised the urgent need to continue assisting Ukraine. Addressing a meeting of European conservative party leaders in Bucharest, he said: “I think that we all have a message for the Kremlin: we will not be intimidated, we will continue to support Ukraine and its brave citizens for as long as necessary. And we remain united on this issue.”

“I think for us it was the best, most vivid reminder that a real war is happening here,” the Greek leader told reporters, saying the missile struck as Zelenskiy was showing him the extent of the damage Odesa’s port infrastructure had sustained as a result of increased bombardment in recent days. “And that’s an additional reason why all European leaders should come to Ukraine because it’s one thing to see and hear what is happening through the media or from President Zelenskiy, with whom we are in regular contact, and quite another for someone to experience war first-hand.”

There was immediate international outrage over the attack. The European Commission president, Ursula von der Leyen, deplored what she described as Moscow’s “new attempt at terror”. “More than ever, we stand by Ukraine,” she said. The European Council president, Charles Michel, condemned the strike as “another sign of Russia’s cowardly tactics”, which he said were “below even the Kremlin’s playbook”.

In Washington, the White House, which has been struggling to end Republic stonewalling of new US aid packages to Ukraine, described the Odesa attack as proof of the war-torn country’s need for military assistance. “This strike is yet another reminder of how Russia is continuing to attack Ukraine recklessly every single day,” said a spokesperson for Joe Biden’s national security council.

The attack came just days after 12 people, including five children, were killed when a Russian drone hit a residential block in the same Black Sea city, one of the deadliest attacks on civilians in weeks.

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Authorities in the Russian-occupied city of Berdiansk in southern Ukraine blamed Kyiv for a car bombing that it said had killed a local election official. “A homemade explosive device was planted under the vehicle of a member of the precinct election commission,” the investigative committee said in a statement.

“The victim died from her injuries,” it added, publishing a video of a blown-out small beige car parked on a dirt track.

The attack came as early voting got under way across occupied Ukraine for this month’s Russian presidential election.

The Moscow-installed head of the Zaporizhzhia region, Yevgeny Balitsky, blamed Ukrainian authorities for the attack and said they were trying to “intimidate” residents ahead of the ballot.

A number of Russian-installed officials have been targeted since Moscow launched its full-scale military operation in Ukraine two years ago. Russia also said Ukraine hit a fuel tank at a metals plant in the Russia’s Kursk region in an early-morning drone strike.

From the start of the conflict, Athens has staunchly stood by its Nato allies despite traditionally strong political, economic and cultural ties with fellow Orthodox Russia and polls showing widespread disapproval among Greeks of support for Ukraine.

Greece was among the first EU member states to send weapons to Kyiv. The stance has dismayed Moscow with Russian officials openly berating Mitsotakis’s centre-right government for its policies.

Last week, the Russian foreign ministry spokesperson said Athens’ “leadership will need to account to the Greek people” for its decision to dispatch arms to Ukraine.