Russia's latest strike on Odesa on Sunday killed two people and severely damaged a historic Orthodox cathedral, drawing a vow of retaliation from Ukraine's leader.

In Russian, Russian President Vladimir Putin claimed Kyiv's counteroffensive had "failed" as he met his closest ally, Belarus leader Alexander Lukashenko, in Saint Petersburg.

The 18th-century Transfiguration Cathedral, the biggest Orthodox church in Odesa, lies within the UNESCO-protected historic city centre.

UNESCO condemned the "brazen" attack on Odesa, which hit several sites in the port city's World Heritage centre. The attack marked "an escalation of violence against (the) cultural heritage of Ukraine", said UNESCO chief Audrey Azoulay.

The strike on Odesa, which Russia has pounded since quitting the Black Sea grain deal last week, came just hours before Russian President Vladimir Putin met his Belarus counterpart for talks.

On the Black Sea in Odesa, locals looked in disbelief as the Transfiguration Cathedral -- originally built in 1794 under imperial Russian rule -- was hit.

Clergymen rescued icons from rubble inside the badly damaged shrine, which was demolished under Stalin in 1936 and rebuilt in the 1990s after the collapse of the Soviet Union. 

Ukraine said it had been "destroyed twice: by Stalin and Putin", denouncing the cathedral strike as a "war crime".

President Volodymyr Zelensky vowed retaliation: "They will definitely feel this," he said.

Icons pulled from the rubble

Images showed smashed mosaics on the cathedral floor as workers cleared the rubble. The outside of the building appeared intact. 

"There was a direct hit to the cathedral," said Father Myroslav, the assistant rector of the cathedral. "It completely damaged three altars.

Icons were pulled out from under the rubble and the shrine was "very badly damaged inside", with "only the bell tower intact", he added.

Clergymen said a security guard and a priest getting ready for a morning liturgy were inside during the attack but both survived.

Russia blamed the cathedral damage on Ukrainian air defence. It said it had hit all its intended targets in the Odesa strike, claiming the sites were being used to prepare "terrorist acts" against Russia. 

But local people said Russia had hit ordinary residential areas.

"We have ordinary residential buildings here, where people live," a woman who owns a beauty salon nearby, Tetiana, told AFP. 

"There are no military facilities here. Just simple beauty salons, a marine agency, a groomer. Nothing military here at all." 

Anzhelika Domanska said she ran with her neighbours when she saw the cathedral burning.

The strike came a year after a missile had hit her house in nearby Mykolaiv. 

"It is not a pleasant anniversary," she said. 

Russia launched a wave of attacks on the Black Sea port this week, after exiting a deal allowing the safe passage of cargo ships between Moscow, Kyiv, Istanbul and the UN. 

Ukraine has vowed to find a way to continue exports from the ports and said Sunday repeated Russian strikes on Odesa this week were an attempt to "prevent and  neutralise international efforts to restore the functioning of the "grain corridor." 

Putin meets Lukashenko

As Odesa cleared rubble from the Russian strikes, Putin hosted his ally Lukashenko in his native city of Saint Petersburg -- their first meeting since Minsk helped end a revolt by Russia's Wagner force.

Both leaders were dismissive of the Ukrainian counteroffensive to take back land captured by Russia.

"There is no counteroffensive," Lukashenko said at the meeting, before being interrupted by Putin: "There is one, but it has failed."

The Belarus strongman now hosts Wagner fighters on his territory, after brokering a deal that convinced its leader Yevgeny Prigozhin to end a march on Moscow and exile himself to Belarus. 

"We are controlling what is happening (with Wagner)," he said, thanking Putin for vowing to defend Belarus should it be attacked. 

Wagner's presence in Belarus has rattled EU and NATO member Poland, which has strengthened its border.

On Sunday, Polish Defence Minister Mariusz Blaszczak said a new battalion of sappers would be formed in the country's northeast.

Polish, US, British, Romanian and Croatian soldiers were training "shoulder to shoulder", he said, during a visit to the northeastern city of Augustow.

The comments came two days after Putin said western Poland was a "gift" from Stalin at the end of World War II, when victorious allies decided on the contours of post-war Europe. Warsaw had summoned the Russian ambassador over the remarks.

Both Putin and Lukashenko also accused Warsaw of having territorial ambitions on Ukraine and Belarus.

Ukraine's Foreign Minister Dmytro Kuleba responded quickly on Twitter.

"Putin’s attempts to drive a wedge between Kyiv and Warsaw are as futile as his failing invasion of Ukraine," he wrote.

"Unlike Russia, Poland and Ukraine have learned from history and will always stand united against Russian imperialism and disrespect for international law."

Fighting in Ukraine continued Sunday, with Russia launching 17 cruise missiles and two ballistic missiles, according to the Ukraine army.

"Russian occupants continue to rob civilians, appropriating the grain harvest of Ukrainian civilians," the general staff statement added.