Russian forces thwarted an attempt at another cross-border incursion by Ukraine into southwestern Russia, a local official reported Sunday, months after Kyiv staged a bold assault on its nuclear-armed enemy that Moscow is still struggling to halt.

An “armed group” sought Sunday to breach the border between Ukraine and Russia’s Bryansk region, its governor, Aleksandr Bogomaz, said but was beaten back. Bogomaz did not clarify whether Ukrainian soldiers carried out the alleged attack, but claimed on Sunday evening that the situation was “stable and under control" by the Russian military.

There was no immediate acknowledgement or response from Ukrainian officials.

The region neighbors Kursk province, where Ukraine launched a surprise push on Aug. 6 that rattled the Kremlin and constituted the largest attack on Russia since World War II. Hundreds of Russian prisoners were blindfolded and ferried away in trucks in the opening moments of the lightning advance, and Ukraine’s battle-hardened units swiftly pressed on across hundreds of square miles (square kilometers) of territory.

Responsibility for previous incursions into Russia’s Belgorod and Bryansk regions has been claimed by two murky groups: the Russian Volunteer Corps and the Freedom of Russia Legion.

Russian officials and state media have sought to downplay the significance of Kyiv’s thunderous run in Kursk, but the country’s forces have so far been unable to dislodge Ukrainian troops from the province. Western officials have speculated that Moscow may send troops from North Korea to bolster its effort to do so, stoking the almost three-year war and bringing geopolitical consequences as far away as the Indo-Pacific region.

Russian lawmakers Thursday ratified a pact with Pyongyang envisioning mutual military assistance, a move that comes as the U.S. confirmed the deployment of 3,000 North Korean troops to Russia.

North Korean units were detected Wednesday in Kursk, according to Ukraine’s Main Intelligence Directorate, known by its acronym GUR. The soldiers had undergone several weeks of training at bases in eastern Russia and had been equipped with clothes for the upcoming winter, GUR said in a statement late Thursday. It did not provide evidence for its claims.

Also on Sunday, Russian President Vladimir Putin said Moscow is working on ways to respond if the U.S. and its NATO allies allow Ukraine to strike deep inside Russia with long-range Western missiles.

Putin told Russian state TV that it was too early to say exactly how Moscow might react, but the defense ministry has been mulling a range of options.

Russia has repeatedly signaled that it would view any such strikes as a major escalation. The Kremlin leader warned on Sept. 12 that Moscow would be “at war” with the U.S. and NATO states if they approve them, claiming military infrastructure and personnel from the bloc would have to be involved in targeting and firing the missiles.

He reinforced the message by announcing a new version of the nuclear doctrine that considers a conventional attack on Russia by a nonnuclear nation that is supported by a nuclear power to be a joint attack on his country — a clear warning to the U.S. and other allies of Kyiv.

Putin also declared the revised document envisages possible nuclear weapons use in case of a massive air attack, opening the door to a potential nuclear response to any aerial assault — an ambiguity intended to deter the West.

Ukrainian leaders have repeatedly said they need permission to strike weapons depots, airfields and military bases far from the border to motivate Russia to seek peace. In response, U.S. defense officials have argued that the missiles are limited in number, and that Ukraine is already using its own long-range drones to hit targets farther into Russia.

That capability was evidenced by a Ukrainian drone strike in mid-September that hit a large Russian military depot in a town 500 kilometers (300 miles) from the border.

The U.S. allows Kyiv to use American-provided weapons in more limited, cross-border strikes to counter attacks by Russian forces.

In a separate update, Bryansk Gov. Bogomaz claimed that over a dozen Ukrainian drones were shot down over the region on Sunday. Separately, a total of at least 16 drones were downed over other Russian regions, including the Tambov province some 450 kilometers (290 miles) north from the border, officials reported. There were no reports of casualties from any of the alleged attacks.

In Ukraine’s southern city of Kherson, Russian shelling killed three civilians on Sunday, local Gov. Oleksandr Prokudin claimed. Another Kherson resident died in a blaze sparked by shells hitting a high-rise, according to Ukraine’s Emergency Service.

Air raid sirens wailed for over three hours in Kyiv overnight into Sunday, and city authorities later reported that “around 10” drones had been shot down. They said no one had been hurt. Ukraine’s air force on Sunday reported that it had shot down 41 drones launched by Russia across Ukrainian territory.