The threat of intensified attacks on Kyiv came after Russian authorities accused Ukraine of launching airstrikes on residential buildings in Bryansk, a region that borders Ukraine, and wounding seven people. Authorities in another border region of Russia also reported Ukrainian shelling Thursday.
Life in Kyiv has been gradually returning to some normalcy after Russia failed to capture the capital and withdrew its troops in northern Ukraine to focus on a concentrated assault in the country's east. A renewed bombardment could return the city's residents to sheltering in subway stations and the steady wail of air raid sirens.
Ukrainian officials have not confirmed striking targets in Russia, and the reports by Russian authorities could not be independently verified. However, Ukrainian officials claimed their forces struck a key Russian warship with missiles on Thursday. If true, the claim would represent an important victory.
The guided-missile cruiser Moskva, named for the Russian capital, sank while being towed to port 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, and its removal reduces Russia's firepower in the Black Sea. The warship's loss in an invasion already widely seen as a historic blunder also was a symbolic defeat for Moscow as its troops regroup for an offensive in eastern Ukraine after retreating from much of the north.
During the first days of the war, the crew of the Moskva reportedly called on Ukrainian soldiers stationed on Snake Island in the Black Sea to surrender in a standoff. A widely circulated recording featured a Ukrainian soldier saying in response: ``Russian warship, go (expletive) yourself.''
The Associated Press could not independently verify the Snake Island incident, but Ukraine and its supporters consider it an iconic moment of defiance. The country recently unveiled a postage stamp commemorating it.
If Ukraine hit the Moskva with missiles, the cruiser likely represents the largest warship to be sunk in combat since the 1982 Falklands War, which saw a similar-sized cruiser called the ARA General Belgrano torpedoed by a British submarine, killing over 300 sailors on board.
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.''
Listing the ways Ukraine has defended against the onslaught, Zelenskyy mentioned ``those who showed that Russian warships can sail away, even if it's to the bottom'' of the sea. It was his only reference to the Moskva.
News about the flagship overshadowed Russian claims of advances in the southern port city of Mariupol, where Moscow's forces have been battling the Ukrainians since the early days of the invasion in some of the heaviest fighting of the war _ at a horrific cost to civilians.
Dwindling numbers of Ukrainian defenders in Mariupol are holding out against a siege that has trapped well over 100,000 civilians in desperate need of food, water and heating. David Beasley, executive director of the U.N. World Food Program, told AP in an interview Thursday that people are being ``starved to death'' in the besieged city.
Mariupol's mayor said this week that more than 10,000 civilians had died and the death toll could surpass 20,000.
Mariupol's capture is critical for Russia because it would allow its 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.
The Russian military continues to move helicopters and other equipment into place for such an effort, according to a senior U.S. defense official, and it is likely to add more ground combat units soon. But it's still unclear when Russia might launch a full-scale campaign in the Donbas.
Moscow-backed separatists have been battling Ukraine in the region since 2014, the same year Russia seized Crimea. Russia has recognized the independence of the rebel regions in the Donbas.
Maksym Marchenko, governor of the Odesa region, said Ukrainian forces struck the Moskva with two Neptune missiles and caused ``serious damage.''
Russia's Defense Ministry said ammunition on board detonated as a result of a fire, without saying what caused the blaze. It said the ``main missile weapons'' were not damaged and that the crew, usually numbering about 500, abandoned the vessel. It wasn't clear if there were any casualties. In addition to the cruise missiles, the warship also had air-defense missiles and other guns.
The Neptune is an anti-ship missile that was recently developed by Ukraine based on an earlier Soviet design. The launchers are mounted on trucks stationed near the coast, and, according to the Washington-based Center for Strategic and International Studies, 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.
Launched as the Slava in 1979, the cruiser saw service in the Cold War and during conflicts in Georgia and Syria, and helped conduct peacetime scientific research with the United States. During the Cold War, it carried nuclear weapons.
British defense officials said the Moskva's loss would likely force Moscow to change the way its naval forces operate in the Black Sea. In a social media post Friday, the U.K. Ministry of Defense said the ship, which returned to operational service last year after a major refit, ``served a key role as both a command vessel and air defense node.''
The sinking ``means Russia has now suffered damage to two key naval assets since invading Ukraine, the first being Russia's Alligator-class landing ship Saratov on 24 March. Both events will likely lead Russia to review its maritime posture in the Black Sea,'' the British ministry said.
On Thursday, other Russian ships in the northern Black Sea moved farther south after the Moskva incident, said a senior U.S. defense official who spoke on condition of anonymity to discuss internal military assessments.
While the U.S. was not able to confirm Ukraine's claims of striking the warship, U.S. national security adviser Jake Sullivan called it ``a big blow to Russia.``
``They've had to kind of choose between two stories: One story is that it was just incompetence, and the other was that they came under attack, and neither is a particularly good outcome for them,'' Sullivan told the Economic Club of Washington.
Russia invaded Feb. 24 and has lost potentially thousands of fighters. 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.