Kursk, Russia - Russia was battling a major cross-border incursion from Ukraine for a second day on Wednesday, with authorities evacuating several thousand civilians due to fighting, officials said.

The incursion began on Tuesday morning, with Russia's defense ministry announcing it had deployed air and artillery firepower to repel Ukrainian troops breaking into the western Kursk region.

President Vladimir Putin accused Kyiv of attacking civilian buildings and said he was meeting security service chiefs to discuss a response.

"The Kyiv regime has undertaken another large-scale provocation," he said in a televised meeting with government officials on Wednesday.

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"It is firing indiscriminately from various types of weapons, including rockets, at civilian buildings, residential houses and ambulances," he added.

At least five civilians have been killed and 24 wounded since the operation began, 13 of whom have been hospitalized, according to Russian officials.

The Russian defense ministry said hostilities were ongoing at noon on Wednesday but stressed "the enemy's movement further into Russian territory had been prevented."

Authorities have evacuated several thousand people from the region and cancelled all mass gatherings, Kursk regional governor Alexei Smirnov said.

"Over the course of the last day, with our help, several thousand people left the shelling zone by personal transport," Smirnov said in a video message on Telegram, adding: "The situation in the region is under control".

Ukraine has not claimed responsibility for the incursion, the most serious in months, as it struggles to halt the advance of Russian forces on its own territory.

However, a security source in Ukraine told AFP that Kyiv had struck a Russian helicopter using a drone on Tuesday over the Kursk region.

Ukrainian presidential aide Mykhailo Podolyak also alluded to the attacks, on social media, without specifically mentioning them. Moscow had used its "border regions with impunity for massive air and artillery attacks," he said.

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Kursk sits just across from Ukraine's northeastern Sumy region and has been subjected to regular Ukrainian shelling attacks since the conflict began in February 2022.

Rybar, a Russian Telegram channel with military links, said Ukrainian forces had made small inroads across the border and occupied several small settlements.

It said Kyiv's troops had reached the outskirts of Sudzha, a town of about 5,000 people some five miles from the border, but that Russian forces had pushed them back.

Fighters from Ukraine have made several brief incursions into Russia before, some by units of Russians fighting in support of Kyiv – the Russian Volunteer Corps and the Freedom of Russia Legion.