Russia's military said Tuesday it quashed what appeared to be one of the most serious cross-border attacks from Ukraine since the war began, claiming to have killed more than 70 attackers in a battle that lasted around 24 hours.

Moscow blamed the raid that began Monday on Ukrainian military saboteurs. Kyiv portrayed it as an uprising against the Kremlin by Russian partisans. It was impossible to reconcile the two versions, to say with certainty who was behind the attack or to ascertain its aims.

The battle — which took place in southwest Russia's Belgorod region, about 80 kilometers (45 miles) north of the city of Kharkiv, in eastern Ukraine — was a fresh reminder of how Russia itself remains vulnerable to attack, along with Russian-occupied regions of Ukraine.

The region is a Russian military hub holding fuel and ammunition depots and was included in Russian President Vladimir Putin's order last year to increase the state of readiness for attacks and improve defenses.

Kremlin spokesman Dmitry Peskov refused to say how many attackers were involved in the assault or comment on why efforts to put down the attackers took so long.

Such cross-border attacks embarrass the Kremlin and highlight the struggles it faces in its bogged-down invasion of Ukraine.

The Belgorod region, like the neighboring Bryansk region and other border areas, has witnessed sporadic spillover from the war, which Russia started by invading Ukraine in February 2022.

Far from the 1,500-kilometer (932-mile) front line in southern and eastern Ukraine, Russian border towns and villages regularly come under shelling and drone attacks, but this week's attack is the second in recent months that also appears to have involved an incursion by ground forces. Another difference from earlier cross-border attacks is that Russia's effort to repel it continued into a second day for the first time.

Russian Defense Ministry spokesman Igor Konashenkov claimed local troops, air strikes and artillery routed the attackers.

“The remnants of the nationalists were driven back to the territory of Ukraine, where they continued to be hit by fire until they were completely eliminated,” Konashenkov said, without providing evidence. He did not mention any Russian casualties.

Russian forces destroyed four armored combat vehicles and five pickup trucks the attackers used, he said. Local officials alleged the invaders also used drones and artillery.

The governor of the Belgorod region, Vyacheslav Gladkov, said the raid targeted the rural area around Graivoron, a town about 5 kilometers (3 miles) from the border. Twelve civilians were wounded in the attack, he said, and an older woman died during an evacuation.

The Russian news portal RBK, quoting unidentified sources in the regional interior ministry and territorial police, said Graivoron came under heavy shelling that lasted about five hours early Monday. After that, tanks fired at the Graivoron border checkpoint while the adjacent village of Kozinka came under mortar and rocket fire, RBK said, citing the same sources. Gladkov later reported that a Koznika villager had been killed.

The attacking force was made up of 10 armored vehicles and an unspecified number of troops, RBK said.

Earlier Tuesday, the regional governor urged residents who had evacuated not to return home until they received official instructions to do so. He said a “counterterrorism operation” was completed by early Tuesday evening.

Gladkov also said fire from the Ukrainian side of the border on Tuesday hit the Borisovka area, about 20 kilometers (20 miles) northeast of Graivoron. No casualties were reported, he said without elaborating on the incident.

The regional governor complained in a video late Tuesday that federal authorities' claims for the past year that “everything is under control” do not ring true in light of this attack and prior assaults. He appealed again to the Kremlin to strengthen defenses.

Since the war began, drones, explosions and missiles have hit fuel and ammunition depots, railroad equipment, bridges and air bases on Russian territory and Russia-occupied areas of Ukraine. Assassinations of Russian-appointed government officials and other public figures have also taken place in those areas.

Ukraine said Russian citizens belonging to murky groups called the Russian Volunteer Corps and the Freedom of Russia Legion were behind the assault.

Ukrainian Deputy Defense Minister Hanna Maliar said the attackers were Russian dissidents unhappy about Putin’s policies.

“These are Russian patriots, as we understand it. People who actually rebelled against the Putin regime,” she said.

The Freedom of Russia Legion said on Telegram the goal was to “liberate” the region.

The Russian Volunteer Corps implied on Telegram that the attack was over, adding: “One day, we’ll come to stay.” The post went up at around the same time as the Russian Defense Ministry claimed to have quashed the assault.

The U.K. Defense Ministry said it was “highly likely” that Russian security forces were fighting partisans in at least three locations in Belgorod.

“Russia is facing an increasingly serious multi-domain security threat in its border regions, with losses of combat aircraft, improvised explosive device attacks on rail lines and now direct partisan action,” it said Tuesday.

Russia’s Investigative Committee, its top law enforcement agency, announced an investigation into alleged terrorism and attempted murder in connection with the raid.

Belgorod officials earlier this year said they had spent nearly 10 billion rubles ($125 million; 116 million euros) on fortifications to protect the region.

Peskov, the Kremlin spokesman, said the raid “elicits deep concerns” and that a "bigger effort” was required to prevent future attacks.

The Russian Volunteer Corps claimed to have breached the border in early March. The shadowy group describes itself as “a volunteer formation fighting on Ukraine’s side.” It's not clear if it — or the Freedom of Russia Legion — has any ties with the Ukrainian military.

Elsewhere, Ukrainian forces made minor progress against Russian forces on the edge of Bakhmut, the eastern Ukrainian city that Moscow claims to have captured, according to Maliar, the Ukrainian deputy defense minister.

She said Tuesday that Ukrainian troops still controlled the southwestern outskirts of the city and that fighting was continuing in the suburbs, on Russia’s flanks.