President Volodymyr Zelenskyy toured the northeastern Ukrainian region of Sumy on Thursday in his first visit to the border area since his forces entered Russian territory more than two weeks ago.

After a meeting with Ukraine’s military commander, Zelenskyy said Ukrainian forces have claimed control of another settlement in the Russian region of Kursk and taken more Russian prisoners of war whom he hopes to exchange for captured Ukrainians. He referred to that as Ukraine’s “exchange fund.”

“Another settlement in the Kursk region is now under Ukrainian control, and we have replenished the exchange fund,” Zelenskyy wrote on the social media platform X after hearing a report from the military commander, Col Gen Oleksandr Syrskyi.

But the gains there come as Ukraine continues to lose ground in its eastern Donetsk region. The Russian Defence Ministry announced Thursday that its military has claimed control of the village of Mezhove.

Ukraine’s push into Russia marks the first capture of Russian territory since World War II. It comes as both sides in the war use drones to attack far within enemy lines.

A Ukrainian drone attack Thursday sparked a fire at a military facility in southern Russia as Kyiv pushes its offensive in the Kursk region and struck key infrastructure including bridges.

Andrei Bocharov, governor of the Volgograd region, said Thursday that a “defence ministry facility” was on fire after being attacked by drones in the area of Marinovka, in a sign that Ukraine is not letting up on its attacks. He did not specify what was damaged.

Ukraine attacked Russia overnight with 28 drones, Russia’s Ministry of Defence said. Thirteen were shot down over the Volgograd region, seven over the Rostov region, four over the Belgorod region, two over the Voronezh region, and one each over the Bryansk and Kursk regions, the ministry said. Russian Telegram channels said drones attempted to attack a military air base near Marinovka in the village of Oktyabrsky. Videos shared on Russian social media showed an explosion in the night sky, reportedly near the base. Marinovka is about 300 km (185 miles) east of the Ukrainian border and about the same distance west from the border with Kazakhstan.

Ukraine claimed responsibility for the attack.

Ukraine’s Security Service and the Special Operation Forces of the Armed Forces of Ukraine conducted the drone attack Wednesday night striking the Marinovka airfield in Russia, a law enforcement official told The Associated Press. The official spoke on condition of anonymity because he was not authorised to speak publicly.

The attack came as the ground offensive in Russia’s Kursk region rattles the Kremlin. The daring operation could involve as many as 10,000 Ukrainian troops backed by armour and artillery, military analysts say.

The Baza Telegram channel, which is close to Russian law enforcement, said one drone was taken down several km (miles) from the airfield near Marinovka and that wreckage from another fell on a trailer near the air base, causing it to catch fire.

Data from NASA fire satellites, which monitor Earth for forest blazes, showed fires breaking out around the air base’s apron, where fighter jets were previously seen parked.

Another fire burned Thursday in Russia’s Rostov region, where firefighters struggled for the fifth day to put out a fire at an oil depot in the town of Proletarsk caused by a Ukrainian drone attack Sunday.

Russian state television channels have largely avoided covering the attack. Russian Orthodox priests visited Proletarsk to pray for injured firefighters.

Independent Russian Telegram channels said another powerful explosion was heard Wednesday evening and shared videos of a fireball burning in the night sky. State news agency Tass said 47 people were injured while putting out the blaze, but firefighters succeeded in stopping fires in six fuel tanks.

Satellite photos from Planet Labs PBC analysed Thursday by The Associated Press showed the fire at the oil depot still intensely burning as of Wednesday. Storage tanks at the facility appeared engulfed in flames. Visible flames could be seen in the images, with a thick black smoke cloud drifting west over the city of Proletarsk.

Kursk’s acting governor, Alexei Smirnov, said authorities began putting up concrete shelters at bus stops and other locations around the city Thursday to protect from shelling.

He said similar work will be done in Zheleznogorsk and Kurchatov, where the Kursk nuclear power plant is located.