Ukraine scored a major success on Tuesday when it struck a Russian warship at port in Crimea, one of the most significant attacks against Moscow’s Black Sea Fleet in months. But in another setback for their ground campaign, Ukrainian officials acknowledged that they had all but retreated from the eastern city of Marinka after a monthslong battle to defend it.

The two developments underscored the diverging fortunes of the two combatants this winter in a war that has largely settled into a deadlock: Ukraine racking up naval successes in the Black Sea and Crimea, where it is putting Russia on the defensive, and Russia pressing its attack on battlefields in the east after blunting a Ukrainian counteroffensive.

A day after Russia said it had taken complete control of Marinka, Gen. Valery Zaluzhny, Ukraine’s top military commander, spoke in sober terms about the fight, comparing it to the scorched-earth battle for Bakhmut, the eastern city that fell to Russia in May. Like Bakhmut, Marinka held limited strategic value, but is now a trophy in ruins for Moscow.

“The situation is exactly the same as it was in Bakhmut,” General Zaluzhny said at a news conference. “Street by street, block by block, and our soldiers were being targeted. And the result is what it is.”

Ukraine’s forces, he said, have retreated to the outskirts of the city and set up some positions behind it, indicating that the cost of staying and fighting was too high. Every inch of Ukrainian land is vital, General Zaluzhny said, but “the lives of our fighters are more important to us.”

Hours earlier, the Ukrainian Air Force said that it had destroyed the Novocherkassk, a large landing ship, in the Crimean port of Feodosia overnight. Russia’s Defense Ministry told the Tass state news agency that the ship had been damaged in an attack using “aircraft-guided missiles,” but did not say whether the vessel had been permanently disabled.

Videos of the attack that appeared to be taken by residents and were released by the Ukrainian Air Force show a huge explosion that produced a large fireball, followed by a giant cloud of smoke and flames billowing into the night sky. The footage could not be immediately verified, but Sergei Aksyonov, the Russian-installed governor of Crimea, said that the attack had started a fire in Feodosia. One person was killed and two others were wounded in the assault, he said.

“The fleet in Russia is getting smaller and smaller!” Mykola Oleshchuk, the commander of Ukraine’s Air Force, wrote in a post on the Telegram messaging app celebrating the strike. He noted that last year, Ukrainian missiles sank the flagship of Russia’s Black Sea Fleet.

The strike on the Novocherkassk came on the heels of another gain for Ukrainian forces: The military said it had shot down five Russian fighter jets in three days. Analysts said that the downing of the bombers — one of the biggest weekly losses for the Russian Air Force since the war began — could ease the pressure on Ukrainian troops operating in some of the hottest spots on the front line.

The Ukrainian military has long maintained that the war cannot be won without taking aim at Russian assets and operations in Crimea, which Moscow illegally annexed in 2014. In recent months, Ukraine has sharply accelerated the pace of strikes on the peninsula, which Russia’s military uses as a logistics hub for its hold on southern Ukraine — stockpiling fuel, ammunition and other supplies to be funneled to the battlefields — and as a launchpad for attacks.

The Black Sea Fleet has fired devastating precision cruise missiles at cities and towns deep inside Ukraine. In an attempt to reduce the threat, the Ukrainian military has repeatedly targeted the fleet this year — damaging a warship in August and hitting the fleet’s headquarters a month later.

Those attacks were significant achievements for a country without warships of its own, and rare successes in a year marked by failed efforts to break through Russian defensive lines on the battlefield.

The battle for Marinka illustrated a defining feature of Russia’s invasion, one that analysts say gives Moscow’s forces a big advantage: Its willingness to send wave after wave of troops into fierce assaults, accepting a staggering number of casualties but counting on superior numbers in soldiers and ammunition to wear down the enemy.

It is the same approach Russia has taken in the nearby city of Avdiivka, where it has been attacking for months in the face of fierce Ukrainian resistance. The Russian assaults come as Ukraine is encountering dwindling support from Western allies.

A suburb of Donetsk, Marinka once had a population of 10,000 and streets lined with schools, shops and even a museum. Today no civilians are left and the place has been reduced to rubble.

“Ukrainian forces held Marinka for almost two years as the Russians annihilated it street by street, and then house by house,” General Zaluzhny said on Tuesday.

Geolocated footage shows that Russian forces attacked Ukrainian positions over months of battle. Then on Monday, Russia said it had seized full control of the town.

The capture of Marinka could allow Russian forces to turn their sights to the nearby towns of Kurakove, Vuhleda and Pokrovsk, bringing them closer to achieving Russia’s goal of capturing the entire Donbas region. General Zaluzhny said Ukrainian troops had “prepared a defensive line outside” Marinka, suggesting that his military would try to thwart Russia’s efforts to advance farther.

The Ukrainian Air Force said that it had used cruise missiles in Tuesday’s Black Sea attack, which took place around 2:30 a.m. local time. Russia’s Defense Ministry told Tass that two Ukrainian Su-24 fighter jets involved in the attack on Feodosia had been “destroyed,” a claim that Ukraine’s military denied.

While the extent of the damage to the ship was not immediately clear, the attack hit what appeared to be a valuable target.

The 360-foot-long Novocherkassk was capable of transporting up to 10 tanks and several hundred troops, according to Russian news media, which reported that it had previously been involved in Russian military operations in Syria. In June 2022, Tass said the ship was part of a group of 12 vessels “ready to perform combat tasks in the Black Sea.”

Ukraine’s military said on Tuesday that it suspected that the ship was carrying attack drones for use in the war. Natalia Humeniuk, a spokeswoman for the Ukrainian army, said on national television that “it is clear that such a large detonation was caused not just by fuel or ammunition of the ship itself.”

Andrii Klymenko, the head of the Black Sea Institute of Strategic Studies, agreed. “Judging by the video of the explosion, which was very powerful, it was carrying explosives: either shells or missiles, or, as some people say, drones,” he wrote in a text message.

Mr. Klymenko noted that the port of Feodosia was close to Cape Chauda, which he said Russia has long used as a launch site for attack drones.

Data compiled by the institute shows that the Ukrainian military carried out at least 155 attacks on Crimea and the Russian Black Sea Fleet from January to October of this year, averaging one every other day.

Amid the intensified campaign, Russia relocated vessels from Sevastopol, the fleet’s home port, to harbors farther away from Ukrainian land, including Feodosia, which is on Crimea’s eastern coast. But Tuesday’s attack made it clear that those ports were still at risk.

The strike came as Ukraine signaled that it was girding for a protracted war against Russia. On Monday, the government introduced a bill in Parliament that proposes lowering the age of people who can be drafted into the military to 25 from 27.

As the Ukrainian Army suffers from a shortage of troops to battle Russia’s repeated assaults, the conscription process has come under scrutiny amid reports of wrongful draft notices and coercive mobilization tactics.

Military officials have said in recent days that a large-scale mobilization of up to 500,000 soldiers will be necessary. President Volodymyr Zelensky of Ukraine said a plan still had to be drawn up before he could make a decision. Although General Zaluzhny did not specify any figures on Tuesday, he called for mobilizing more troops to cover Ukrainian losses.