As Ukrainian forces fight to isolate a large group of Russian soldiers caught between a river in Russia’s Kursk Province and the Ukrainian border, Kyiv has launched a series of strikes at airfields, ports and oil depots in Russia aimed at degrading the Kremlin’s war effort.

A Ukrainian missile strike on the Russian port of Kavkaz hit a large cargo ferry laden with fuel on Thursday, triggering a towering blaze at the facility, according to Russian and Ukrainian officials as well as video posted to social media channels. Kavkaz is one of the country’s largest passenger ports and the main ferry terminal connecting Russia with Crimea.

“This ferry is one of the key links in the Russian military logistics chain, primarily for supplying the occupying forces with fuel and lubricants, but it also transported weapons,” a Ukrainian Navy spokesman, Dmytro Pletenchuk, said in a statement.

The attack on the transit hubs came after strikes on the only bridge linking Crimea to Russia over the Kerch Strait left it damaged, forcing Moscow to increasingly rely on large ferries capable of carrying rail cars to support its occupation forces on the peninsula, which it annexed in 2014.

“The ferry sank, effectively blocking the operation of this part of the port,” Mr. Pletenchuk said. “They still have one platform left for loading rail cars onto ferries. However, there are no ferries available.”

The RIA state news agency of Russia, citing emergency services, said a fire sparked by the attack had “practically” not affected the port’s infrastructure, but that the ferry struck by Ukraine was half submerged. It was not possible to independently assess the extent of the damage.

Ukraine has stepped up its efforts to attack inside Russia, most notably in the cross-border incursion in the North, but also with strikes on energy depots and supply routes, as a counter to its struggles in the Eastern Donbas region, where its forces are being pushed back under a withering Russian assault.

In recent days, Moscow’s troops have seized at least three settlements, closing in on Pokrovsk, a logistics hub for the Ukrainian Army in the region. With the city of roughly 60,000 people now under threat of Russian artillery, Ukrainian officials have urged civilians to leave.

While the Kremlin is moving reinforcements to the area in hopes of blunting the Ukrainian advance, it has made clear that it will not relax its assault in the East around the cities of Pokrovsk, Toretsk and Niu-York.

“They have a firm position not to withdraw troops” from these offensive operations, Roman Kostenko, the secretary of the defense and intelligence committee in Ukraine’s Parliament, told Ukrainian journalists. “ This is a strategic direction for them, and we now see that even though they realize they have no reserves to recapture Kursk, they are still focusing on the territory of Donetsk.”

Ukraine’s attack on the ferry depot was part of a long-running effort to isolate Russian forces on the peninsula, which served as one of the launchpads for Russia’s full-scale invasion and continued to play an important role in supporting Russian occupation forces in southern Ukraine.

The Ukrainians also targeted the Marinovka military airfield in Russia’s Volgograd region before dawn on Thursday, using long-range drones to hit the base around 180 miles from the Ukrainian border.

The strikes damaged hangars and other facilities at the base, according to satellite imagery verified by military analysts and data from NASA that tracks fires, as well as videos and photographs circulating on social media that have been geolocated by military analysts. A precise damage or casualty toll could not be independently verified.

Andrey Bocharov, the governor of the Volgograd region, claimed “most of the drones” were destroyed and the damage was caused by falling debris.

The assault came as Kyiv increased its attacks on Russian airfields, striking four in western Russia last week.

President Volodymyr Zelensky said the Ukrainian campaign to seize land inside Russia and the long-range strikes were part of a coordinated effort to bring the war to Russians in a way they have not felt to date.

“We must all understand that to drive the occupier from our land, we must create as many problems for the Russian state as possible on its own territory,” he said on Thursday at a forum for military veterans. “This heroic work is becoming more precise, more long-range, and more effective.”

President Vladimir V. Putin of Russia has sought to distance himself from loss of hundreds of square miles of Russian territory. Speaking during an online meeting with politicians, including the governors of the Kursk, Belgorod and Bryansk regions on Thursday, the Russian leader described the territorial losses there as “security issues,” asserting that the “problems” in Kursk “are the responsibility of the security forces.”

Alexei Smirnov, the acting governor of Kursk region, reported that around 133,000 civilians had evacuated from border areas of the region, while around 20,000 still remained.

Ukrainian officials hope the battlefield calculations for the Russians will become more complicated as Ukraine’s forces threaten to encircle a large grouping of Russian soldiers now caught between the western reaches of the Seym River and the Ukrainian border.

This week, the last of three bridges spanning the meandering waterway was destroyed. Russia has responded by building temporary crossings, but they have been quickly targeted by Ukrainian artillery and drones, according to combat footage verified by military analysts.

Ukrainian officials have speculated that as many as 3,000 Russian soldiers could be trapped in a 270-square-mile pocket. It is impossible to independently verify how many Russians might be in the area.

Lt. Gen. Mykola Oleshchuk, the commander of the Ukrainian Air Forces, said for the first time on Friday that Kyiv was using its warplanes to fire guided bombs supplied by its Western allies to hit targets inside Russia as part of the Kursk operation.

He released one video showing the destruction of two of the crossings over the Seym this week and another showing an attack on a Russian base.

“This is what the Air Force airstrike with high-precision American GBU-39 bombs looks like on a platoon base in the Kursk region,” he wrote.

Anastasia Kuznietsova contributed reporting.