Russia’s Defense Ministry promised Friday to ramp up missile attacks on the Ukrainian capital in response to Ukraine’s alleged aggression on Russian territory, an ominous warning that followed Moscow’s stinging symbolic loss of its navy’s flagship in the Black Sea.

The threat of intensified attacks on Kyiv came after Russian authorities accused Ukraine of wounding seven people and damaging about 100 residential buildings with airstrikes on Bryansk, a region bordering Ukraine. Authorities in another border region of Russia also reported Ukrainian shelling Thursday.

“The number and the scale of missile attacks on objects in Kyiv will be ramped up in response to the Kyiv nationalist regime committing any terrorist attacks or diversions on the Russian territory,” Russian Defense Ministry spokesman Igor Konashenkov said.

A renewed bombardment could return Kyiv’s residents to the steady wail of air raid sirens heard during the early days of Russia’s invasion and to fearful nights sheltering in subway stations. The capital has displayed tentative signs of pre-war life after Russian troops failed to capture the city and retreated to concentrate on eastern Ukraine, leaving behind evidence of possible war crimes.

Russia previously accused Ukraine of shelling or attacking its border regions. Ukrainian officials have not confirmed striking targets in Russia, and the reports could not be independently verified.

However, Ukrainian officials insist their forces did strike a key Russian warship with missiles. If true, the reported Wednesday attack on the guided-missile cruiser Moskva, named for the Russian capital, would represent an important victory for Ukraine and a symbolic defeat for Russia.

The flagship of Russia’s Black Sea fleet sank while being towed to port Thursday after suffering heavy damage under circumstances that remained in dispute. Moscow acknowledged a fire on board but not any attack. U.S. and other Western officials could not confirm what caused the blaze.

The Moskva had the capacity to carry 16 long-range cruise missiles. If Ukrainian forces took out the vessel, it was likely the largest warship to be sunk in combat since the Falklands War. A British submarine torpedoed an Argentine navy cruiser called the ARA General Belgrano during the 1982 conflict, killing over 300 sailors.

The sinking of the Russian warship reduces Russia’s firepower in the Black Sea, although military analysts disagreed on the event’s significance to the course of the war. Either way, the loss was viewed as emblematic of Moscow’s fortunes in a seven-week invasion widely seen as a historic blunder following the retreat from the Kyiv region and much of northern Ukraine.

“A ‘flagship’ Russian warship is a worthy diving site. We have one more diving spot in the Black Sea now. Will definitely visit the wreck after our victory in the war,” Ukrainian Defense Minister Oleksiy Reznikov tweeted Friday in a likely apocryphal boast.

In his nightly address Thursday, Ukrainian President Volodymyr Zelenskyy told Ukrainians they should be proud of having survived 50 days under Russian attack when the invaders “gave us a maximum of five.”

Russia’s warning of renewed airstrikes did not stop Kyiv residents from taking advantage of a sunny and slightly warmer spring day as the weekend approached. More people than usual were out on the streets Friday, walking their dogs, riding electric scooters and strolling hand in hand.

In one central park, a small group of young people, one draped in a Ukrainian flag, danced to the music of a portable speaker.

News about the Moskva overshadowed Russian claims of advances in the southern port city of Mariupol, which Moscow’s forces have blockaded since the early days of the invasion. Dwindling numbers of Ukrainian defenders have held out against a siege that has come at a horrific cost to trapped and starving civilians.

Mariupol’s mayor said this week that more than 10,000 civilians had died and the death toll could surpass 20,000. Other Ukrainian officials have said they expect to find evidence of atrocities against civilians like the ones discovered in Bucha and other towns outside Kyiv.

The Mariupol City Council said Friday that locals reported seeing Russian troops digging up bodies that were buried in residential courtyards and not allowing new burials “of people killed by them.”

“Why the exhumation is being carried out and where the bodies will be taken is unknown,” the council said on the Telegram messaging app.

Mariupol’s capture would allow Russian forces in the south, which came up through the annexed Crimean Peninsula, to fully link up with troops in the Donbas region, Ukraine’s eastern industrial heartland and the target of the looming offensive.

Moscow-backed separatists have fought Ukrainian forces in the Donbas since 2014, the same year Russia seized Crimea from Ukraine. Russia has recognized the independence of two rebel-held areas of the region.

Although it’s not certain when Russia will launch the full-scale campaign, a regional Ukrainian official said Friday that seven people died and 27 were injured after Russian forces opened fire on buses carrying civilians in the village of Borovaya, near the northeastern city of Kharkiv. The claim could not be independently verified.

Dmytro Chubenko, a spokesman for the regional prosecutor’s office, told Ukraine’s Suspilne news website, that Ukrainian authorities had opened criminal proceedings in connection with a suspected “violation of the laws and customs of war, combined with premeditated murder.”

A large explosion also struck the eastern city of Kramatorsk, where a missile strike on a train station a week earlier killed more than 50 people as thousands heeding warnings to evacuate the Donbas area waited to leave.

Associated Press journalists in Kramatorsk heard the sound of a rocket or missile and then the blast, followed by sirens wailing Friday. It was not immediately clear what was hit or whether there were casualties.

The Russian Defense Ministry said Friday that Russian strikes in the Kharkiv region “liquidated a squad of mercenaries from a Polish private military company” of up to 30 people and “liberated” an iron and steel factor in Mariupol. The claims could not be independently verified.

On Thursday, the Defense Ministry explained the damage to Russia’s Black Sea flagship by a fire had caused ammunition on board to detonate. Apart from the cruise missiles, the Moskva also carried air-defence missiles and other guns.

The ministry did not say what might have caused the blaze but reported that the crew, which usually numbers about 500, abandoned the vessel. It wasn’t clear if there were any casualties.

Maksym Marchenko, governor of Ukraine’s Black Sea region of Odesa, said Ukrainian forces struck the Moskva with two Neptune missiles and caused “serious damage.” The Neptune is an anti-ship missile recently developed by Ukraine based on an earlier Soviet design.

According to the Washington-based Center for Strategic and International Studies, the missile system can hit targets up to 280 kilometers (175 miles) away. That would have put the Moskva within range, based on where the ship was when the fire began.

Other Russian ships in the northern Black Sea moved farther south after the Moskva incident, a senior U.S. defence official said, speaking on condition of anonymity to discuss internal military assessments.

Russia invaded Ukraine on Feb. 24 and has suffered thousands of military casualties. The conflict has killed untold numbers of Ukrainian civilians and forced millions more to flee.

It has also further inflated prices at grocery stores and gasoline pumps, while dragging on the global economy. The head of the International Monetary Fund said Thursday that the war helped push the organization to downgrade economic forecasts for 143 countries.

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Associated Press journalists around the world contributed to this report.

Adam Schreck , The Associated Press