Ukrainian emergency and rescue personnel operate at the site of the destroyed supermarket following a Russian strike, in Kostyantynivka, eastern Donetsk region, on Aug. 9, 2024, amid the Russian invasion of Ukraine. A Russian strike on a supermarket in the eastern Ukrainian town of Kostyantynivka on Friday killed at least 10 people and injured 35, Ukraine's interior minister said. The town is about 13 kilometers (eight miles) from the nearest Russian positions and faces almost daily strikes. (Roman Pilipey/AFP via Getty Images/TNS)

Russia dispatched military reinforcements to confront Ukrainian forces in an ongoing battle in its western Kursk region, the first foreign incursion on its territory since World War II.

The Defense Ministry in Moscow sent tanks, artillery and multiple-rocket launchers to Kursk on a fourth day of fighting against Ukrainian troops, whose surprise cross-border operation is the biggest assault on Russia since President Vladimir Putin ordered the 2022 invasion of Ukraine.

Earlier Friday, Ukraine’s General Staff said it carried out a drone strike on a military airfield in the neighboring Lipetsk region, which targeted a storage facility for glide bombs used by Russia against Ukrainian forces and cities.

Putin looked grim faced at a regular meeting of his Security Council on Friday, though he offered no comment on the crisis that’s spiraling into the most serious wartime challenge to the Kremlin since last year’s short-lived mutiny by Wagner mercenary leader Yevgeny Prighozin.

The Russian Defense Ministry said earlier that its forces used air strikes and artillery to stop Ukrainian troops pushing “deep into” its territory. The authorities in Moscow declared a federal emergency in the Kursk region as thousands of people abandoned their homes to flee the fighting.

While much of the situation on the battlefield remained unclear, Russian military bloggers reported Ukrainian advances as deep as 37 kilometers (23 miles) into the Kursk region.

Video posted on social media appeared to show a column of at least a dozen Russian troop vehicles that had been destroyed in the Rylsk district. The footage couldn’t be independently verified.

Fighting around the town of Sudzha, the site of a key transit point for the last remaining pipeline carrying Russian gas to Europe, helped push European natural gas prices to the highest level this year on fears of possible disruptions to supplies. Flows were reported to be continuing within the normal range.

Ukrainian President Volodymyr Zelenskyy convened a meeting of his war council Friday that he said included the military’s report on “our defensive actions in the directions from which Russia launched attacks on” Ukraine, in a post on the X social media platform.

Officials in Kyiv have remained tight-lipped about the goals of the operation in the Kursk region, which has gained endorsement from Ukraine’s U.S. and European Union allies.

While the U.S. doesn’t support “long-range attacks” into Russia, the intervention in Kursk is consistent with Washington’s policy on Ukraine’s use of American-supplied weapons, Deputy Pentagon Press Secretary Sabrina Singh told reporters.

“Ukraine is fighting a legitimate defensive war against an illegal aggression,” said Peter Stano, lead spokesperson for the EU’s foreign affairs and security policy. “In the framework of this legitimate right to defend itself Ukraine is entitled to hit the enemy wherever it finds necessary on its territory, but also on the territory of the enemy.”

A Russian missile strike in Ukraine’s eastern Donetsk region killed at least 12 people and wounded 44 in the town of Kostyantynivka on Friday, the Interior Ministry in Kyiv said on Telegram.

In Ukraine’s northern Sumy region, bordering Kursk and other Russian regions, officials ordered a mandatory evacuation of as many as 20,000 residents from a 10-kilometer zone under fire.

While the Russian army offensive in eastern Ukraine goes on, the war that’s now in its third year has steadily spread toward Russian territory with Ukrainian forces targeting military objects and energy infrastructure with drones and missiles.

The spectacular operation in Kursk is a boost for Ukrainian army Commander-in-Chief Oleksandr Syrskyi, who’s faced criticism over his leadership, Volodymyr Fesenko, head of the Penta research institute in Kyiv said in a Facebook post.

“We have been waiting for something like this for a long time,” he said.

—With assistance from Volodymyr Verbianyi and Andrea Palasciano.