Russian forces are stepping up their operations in the northern Ukrainian region of Kharkiv, according to Ukrainian officials.

The head of the region's military administration, Oleh Syniehubov, said Kremlin forces have continued shelling several areas around the region, including the city of Kharkiv.

Two men were killed and four people were injured when a non-residential building was struck with a bomb in the village of Kruhliakivka, Syniehubov said.

Russian artillery fire and air strikes along the front line have intensified in recent days.

President Volodymyr Zelensky said Saturday that a blood transfusion center in the region was bombed. He said there are dead and wounded victims as a result of the attack, but did not provide any specific numbers.

CNN cannot independently verify reports about attacks on the front lines in Ukraine.

Dueling claims near Kupyansk: The Russians claimed to have taken a village near Kupyansk on Saturday, but Syniehubov said Ukraine's troops have held their positions in the area. He also said that Russia's attempts to conduct assault operations in villages northeast of Kupyansk had failed.

Ukrainian forces allegedly shelled a university in Russian-held territory with controversial cluster munitions, Russia's state media TASS reported, citing emergency services on the scene.

TASS said that the Donetsk University of Economics and Trade was hit by the weapons, causing a fire to break out. Emergency services said there were no people inside at the time and they are working to put out the fire.

CNN has not been able independently verify the claim.

Donetsk has been plagued by fighting since 2014, when Russia began backing pro-Moscow separatists. The region was one of four territories Russia said it would annex last year in violation of international law.

Understanding cluster munitions: Cluster munitions are particularly dangerous when fired near populated areas because they scatter explosive material, so-called “bomblets,” across large areas, posing a greater threat to nearby civilians than many other types of explosives. Those that fail to explode on impact can detonate years later, posing a long-term risk to anyone who encounters them, similar to landmines.

The danger posed by cluster weapons has prompted more than 100 countries – including the United Kingdom, France and Germany – to sign a treaty prohibiting their use.

Their use in the conflict: Russian forces have been accused of using cluster bombs throughout the conflict, killing at least 200 civilians, the Ukrainian prosecutor general’s office said in a statement on Friday. 

The United States began sending Kyiv American-made cluster bombs last month despite concerns regarding the danger they pose to civilians. US President Joe Biden told CNN's Fareed Zakaria that he approved the shipments because Ukraine was "running out of ammunition."

A Russian guided aerial bomb struck a blood transfusion center in the country's northeastern Kharkiv region Saturday, according to Ukrainian President Volodymyr Zelensky.

He said on Telegram that there are dead and wounded victims as a result of the attack, but did not provide any specific numbers.

Zelensky said the blood transfusion center is located in the Kupyansk community, where Russia has recently amassed troops on the eastern front line. A fire broke out at the center following the attack, he added.

CNN cannot independently verify reports about attacks on the front lines in Ukraine.

The area was liberated in a Ukrainian counteroffensive last fall.

Ukraine has served notice that it intends to continue attacks using maritime drones, following two strikes using such weapons within 24 hours.

The head of the Ukrainian Security Service (SBU) Vasyl Maliuk said Saturday that any explosions that happen to Russian ships or the Crimean bridge are "an absolutely logical and effective step. Moreover, such special operations are conducted in the territorial waters of Ukraine and are completely legal."

Maliuk said that if the Russians wanted such explosions to stop "they have the only option to do so — to leave the territorial waters of Ukraine and our land."

Some context: The Russian-flagged tanker Sig was damaged by a maritime drone overnight near the bridge connecting the annexed Crimean peninsula to mainland Russia. According to the Russian agency for Marine and River Transport, the Sig was hit shortly before midnight Friday local time. It was not carrying a cargo of oil at the time.

The hit on the oil tanker was carried out in a joint operation with the Navy, a Ukraine Security Service (SBU) source told CNN.

The attack came hours after Ukrainian sea drones attacked a major Russian naval base in the Black Sea.

Ukrainian officials are ordering mandatory evacuations for children in nine additional frontline settlements "due to the difficult security situation and hostile shelling."

The government ministry that manages Russian-occupied territories in Ukraine said in a statement Saturday that officials have voted unanimously in favor of the new compulsory evacuations.

They affect a series of towns and villages that dot the eastern Donetsk region: Yampil, Zarichne, Torske, Orihuvatka, Nykonorivka, Malynivka, Tykhonivka, Vasiutynske and Rai-Oleksandrivka.

All are close to the front lines in an area that has seen attacks of growing intensity by Russian forces. The order applies to 130 children, the ministry said.

The ministry also reiterated warnings for civilians to evacuate from a “five-kilometer (about 3-mile) danger zone” in the Sumy region of northern Ukraine. Currently, 1,718 people, including 228 children, have been evacuated from the area bordering Russia.

Ukrainian authorities began issuing compulsory evacuation orders in March 2023 and have added settlements as conditions on the front line change.