Ukraine rushed reinforcements to its northeastern Kharkiv region to hold off a Russian attempt to breach local defenses, authorities said, a tactical switch by Moscow that Ukrainian officials have been expecting for weeks as the war stretches into its third year.

Intense nighttime shelling targeted Vovchansk, in the Kharkiv region and less than 5 kilometers (3 miles) from the Russian border, regional Gov. Oleh Syniehubov said. The barrage prompted authorities to begin the evacuation of around 3,000 people.

Then, around dawn, Russian infantry tried to penetrate the Ukrainian defenses near Vovchansk, Ukraine’s Defense Ministry said, adding that it had deployed reserve units to fend off the attack.

Russian military bloggers said the assault could mark the start of a Russian attempt to carve out a “buffer zone” that President Vladimir Putin vowed to create earlier this year to halt frequent Ukrainian attacks on Belgorod and other Russian border regions.

Ukraine had previously said it was aware that Russia was assembling thousands of troops along the northeastern border, close to the Kharkiv and Sumy regions. While the Kremlin’s forces launched their most recent ground offensive in eastern Ukraine, Ukrainian intelligence officials said they expected the Kremlin’s forces to attack in the northeast, too.

Ukrainian President Volodymyr Zelenskyy said his country’s military had anticipated the attack and had calibrated its response.

“Now there is a fierce battle in this direction,” Zelenskyy was quoted as saying by Ukraine’s public broadcaster Suspilne.

Though Russia likely can’t capture Kharkiv, Ukraine’s second-largest city, it could compel Ukraine to send more troops to the region, leaving other areas more vulnerable to attack. Also, forcing Ukrainian authorities to evacuate civilians is likely to create disruption and divert resources.

“The entire town is under massive shelling now, it is not safe to stay here,” Vovchansk administration head Tamaz Hambarishvili told Ukraine’s Hromadske Radio.

The Ukrainian Defense Ministry said fighting against Russian sabotage and reconnaissance groups continued into the afternoon.

Meanwhile, a Ukrainian long-range drone struck an oil refinery inside Russia on Friday, officials said, a day after what appeared to be the deepest strike by Kyiv’s forces on Russian soil hit a petrochemical facility.

Ukraine has repeatedly targeted refineries, hoping to disrupt the Kremlin’s war machine. Russia is one of the world’s biggest oil producers, providing key revenue and fuel.

A Ukrainian drone hit a refinery near the city of Kaluga, southwest of Moscow, setting four oil storage tanks ablaze, according to Vladislav Shapsha, the regional governor. He said there were no casualties.

The Russian Defense Ministry said that air defenses downed seven Ukrainian drones early Friday in the Moscow, Bryansk and Belgorod regions.

On Thursday, a senior official in Russia’s Bashkortostan region, some 1,300 kilometers (800 miles) from the Ukrainian border, said a drone strike in the city of Salavat caused a fire at a petrochemical facility.

The Russian Emergencies Ministry said a pumping station building on refinery land was damaged but there was no fire. Ukrainian military intelligence refused to comment.

(AP)