Attacks in southern Russia close to the Ukrainian border continued on Tuesday with an explosion reported at a defence factory and skirmishes at a border crossing, a day after anti-Kremlin fighters aligned with Ukraine appeared to have begun a rare ground assault inside Russia.

Russia’s ministry of defence said on Tuesday afternoon that it had pushed the pro-Ukrainian militants back across the border and was continuing to target them, adding that a number of “saboteurs” had been killed. Russia’s claim could not be verified, and people who claimed to represent the pro-Ukrainian fighters maintained that their attacks were ongoing.

The Free Russia Legion, a group of Russians who have taken up arms for Ukraine, has claimed responsibility for the incursion. A representative of the group said on Tuesday that Ukrainian officers were aware of the operation but had not directed it.

But Russian officials have blamed Ukraine’s military, and the Kremlin spokesman, Dmitri S. Peskov, sought to use the attacks to justify Russia’s invasion of Ukraine.

“This once again confirms that Ukrainian militants are continuing their activities against our country,” Peskov told reporters on Tuesday. “This requires a great deal of effort from us, and these efforts are continuing.”

Ukraine has sought to cast the border violence as a sign of internal division in Russia, calling the attackers “opposition-minded citizens of Russia.” Peskov maintained that the fighters — even if they were ethnic Russians — are “Ukrainian militants”.

Earlier on Tuesday, the Russian governor of Belgorod, Vyacheslav Gladkov, said that a “counterterrorism” operation had continued for a second day in the border region. Soldiers and armoured vehicles, including some bearing Ukrainian markings, were seen in videos posted online from Belgorod on Monday and verified by The New York Times. Gladkov said the region had been shelled 15 times on Tuesday morning.

In another Russian border region to the north, Bryansk, a military factory warehouse caught fire on Tuesday near the town of Dyatkovo, local news media reported. Details were not immediately available.

The Free Russia Legion operates under the umbrella of Ukraine’s International Legion, a fighting force overseen by Ukrainian officers. Ukrainian commanders in the International Legion knew about the operation but had not directed it, Ilya Ponomarev, an exiled former member of the Russian parliament who described himself as the political representative of the Free Russia Legion, said in a telephone interview on Tuesday.

The group had captured about a dozen Russian border guards, he said, a claim that could not be verified. He described the incursion as an effort to “liberate a certain part of the Russian land”.

New York Times News Service