(NewsNation) — Ukraine said Thursday that its forces struck and seriously damaged the flagship of Russia’s Black Sea fleet, dealing a potentially major setback to Moscow’s troops as they regroup for a renewed offensive in the east.

The warship eventually sank in the Black Sea on Thursday, according to the Associated Press.

Russia did not acknowledge the attack but said the entire crew of the Moskva, a warship that would typically have 500 sailors on board, was forced to evacuate after a fire overnight and also reported it was badly damaged. The ship carried 16 missiles, and its removal from combat would greatly reduce Russia’s firepower in the Black Sea.

Naval operations and electronic warfare expert Bryan Clark said on “NewsNation Prime” on Thursday night that the damage of this ship may not be a huge blow to the Russian war effort.

“Militarily, it’s not a huge loss because the naval part of the fight has not been that important for Russia up to now,” said Clark, a senior fellow at the Hudson Institute. “They’ve used it for some amphibious assaults but it really hasn’t been decisive.”

Symbolically, the loss of the ship is huge to the Russians, Clark said.

“This was the flagship of the Black Sea fleet. It was in charge of a dozen or so ships that were out in the Black Sea and it was one of their last remaining of their Slava-class cruisers, which are a large-combatant, 15,000-tons, that’s used for a combination of air defense and surface warfare or attacking other ships,” Clark said.

Despite an early report from one Ukrainian official saying the ship had sunk, the Moskva was still moving on its own power, at least for awhile, a senior U.S defense official said earllier Thursday. The official, who spoke on condition of anonymity, said the Pentagon could not confirm what caused the fire.

The ship was about 60 miles out at sea, invisible from the shoreline, when it was struck by the Ukrainians, Clark said. This means they must have had some kind of intelligence provided to them on the location of the vessel, either by unmanned craft or another ship out at sea that had to relay information to the missile battery.

“It was a pretty sophisticated operation for the Ukrainians,” Clark said. “They can certainly draw some confidence they were able to execute it.”

Clark said it was surprising the Russians admitted to the damaging of the ship as quickly as they did and added this will probably be a humiliation for Russia that “they may feel that they need to balance out on the battlefield.”

Retired Col. Mark Cancian of the Center for Strategic and International Studies, appearing on NewsNation’s “Rush Hour,” said that in the short term, the loss of Moskva will likely not impact the conflict with Ukraine. But he described it as a “blow” to Russia’s naval forces.

“This is quite extraordinary. This is one of the largest ships in the Russian Navy. For it to sink is quite a blow and it’s irreplaceable. They’ve stopped making these large surface combatants, so there’s no replacement coming along. It had tremendous capabilities,” Cancian said.

The damage to the warship came on the heels of a visit with leaders from three other EU countries on Russia’s doorstep who fear they could next be in Moscow’s sights. Lithuanian President Gitanas Nausėda declared that “the fight for Europe’s future is happening here.”

Also Thursday, Russia accused Ukraine of sending two low-flying military helicopters across the border and firing on residential buildings in the village of Klimovo in Russia’s Bryansk region, about 7 miles from the frontier. Russia’s Investigative Committee said seven people, including a toddler, were wounded.

Russia’s state security service had earlier said Ukrainian forces fired mortar rounds at a border post in Bryansk as refugees were crossing, forcing them to flee. These reports could not be independently verified.

Meanwhile, President Joe Biden, who called Russia’s actions in Ukraine “a genocide,” approved $800 million in new military assistance to Ukraine.

The new arms package includes 18 of the U.S. Army’s 155mm howitzers and 40,000 artillery rounds, two air surveillance radars, 300 Switchblade “kamikaze” armed drones and 500 Javelin missiles designed to knock out tanks and other armor. Also included are 10 counter-artillery radars used to track incoming artillery and other projectiles to determine their point of origin for counterattacks.

Pentagon press secretary John Kirby said delivery of the material will be expedited.

Despite the flagship damage, Russia claims its forces have advanced in Mariupol, where they have been battling the Ukrainians since the early days of the invasion in some of the heaviest fighting of the war. Thousands of civilians have died. Many remain in the city in dire need of food, water and shelter.

Mariupol’s capture is critical for Russia because it would put a swath of territory in its control that would allow its forces in the south, who came up through the annexed Crimean Peninsula, to link up with troops in the eastern Donbas region, Ukraine’s industrial heartland and the target of the coming offensive.

Moscow-backed separatists have been battling Ukraine in the Donbas since 2014, the same year Russia seized Crimea. Russia has recognized the independence of the rebel regions in the Donbas. Still, the loss of the Moskva, which fires missiles, could set those efforts back.

Maksym Marchenko, the governor of the Odesa region, said the Ukrainians struck the ship with two Neptune missiles and caused “serious damage.” Russia’s Defense Ministry said ammunition on board detonated as a result of a fire and that it was investigating the cause of the blaze.

The Neptune is an anti-ship missile that was recently developed by Ukraine and 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, the missiles can hit targets up to 175 miles away.

Hours after the damage to the ship was reported, Ukrainian authorities said on the Telegram messaging service that explosions had struck Odesa, Ukraine’s largest port. They urged residents to remain calm and said there is no danger to civilians.

Eight weeks ago, Russia invaded on Feb. 24 with the goal, according to Western officials, of rapidly seizing Kyiv, toppling the government and installing a Moscow-friendly replacement. But the ground advance stalled in the face of strong Ukrainian resistance with the help of Western arms. The ongoing conflict has killed untold numbers of Ukrainian civilians and forced millions more to flee.

The war has also unsettled the post-Cold War balance in Europe, and particularly worried countries on NATO’s eastern flank that fear they could next come under attack. As a result, those nations have been strong supporters of Ukraine.

In an overnight address, Zelenskyy noted that the prosecutor of the International Criminal Court visited the Kyiv suburb of Bucha, which was controlled by Russian forces until recently and where evidence of mass killings and more than 400 bodies were found.

“It is inevitable that the Russian troops will be held responsible. We will drag everyone to a tribunal, and not only for what was done in Bucha,” Zelenskyy said late Wednesday.

Peace talks thus far have been unsuccessful. Putin has vowed to press the invasion until his goals are met.