A state of emergency has been declared in the Kursk region of Russia, as a rare cross-border attack by Ukrainian troops continued on Wednesday.

The acting regional governor, Alexei Smirnov, said the move was necessary “to eliminate the consequences of enemy forces coming into the region”.

Russian officials said at least five civilians had been killed and 31 wounded, six of them children, since the start of the incursion.

Ukraine has not officially commented and the depth of the incursion remains unclear.

On Tuesday morning, up to 1,000 Ukrainian troops, as well as 11 tanks and more than 20 armoured combat vehicles, entered Russia near the town of Sudzha, Moscow said.

Fighting reportedly took place in a number of villages throughout Tuesday, with local authorities urging residents to limit their movements and all public events cancelled.

A number of air alerts were issued in Kursk and footage posted online – verified by the BBC – showed fighter jets flying low over the region, with smoke rising from areas on the ground.

Thousands of people were evacuated from border areas and doctors were being drafted in from other cities, Mr Smirnov said.

Ukrainian incursions into Russian territory have been extremely rare since Russia launched its full-scale invasion in February 2022.

On Wednesday evening, Ukrainian MP Oleksiy Honcharenko said the Ukrainian army had established control over the Sudzha gas hub, a major gas facility involved in the transit of natural gas from Russia to the EU via Ukraine, which has continued despite the war.

It is the only point of entry for Russian gas into the EU.

Although the claim has not been verified by the BBC, Mr Honcharenko’s comment was the first confirmation of an incursion into Russian territory by a Ukrainian official.

Mr Honcharenko said on Facebook that while he did not know what the “plan” behind the incursion was, it would show “Europeans and Americans that… Russia can and needs to be attacked”.

Speaking to the BBC’s Newshour, he added that “from a military point of view, we are trying to take back the initiative”.

“We are showing the world that the world should not be scared of escalation or the reaction of Putin. There is no reaction,” he said.

“For the first time since the Second World War, Russian territory that is internationally recognised is occupied and Putin did not [turn] to nukes and so on.”

He said the incursion would also force Russia to move troops to the region and hopefully decrease the number of attacks it can carry out in eastern Ukraine.

A White House spokesperson said the US had no previous knowledge of the attack and that it planned to reach out to the Ukrainian military “to learn more about their objectives”.

In a televised meeting with government officials on Wednesday, Russian President Vladimir Putin accused Ukraine of launching a “major provocation” and “firing indiscriminately” at civilian buildings and residences.

Russia’s Chief of General Staff Valery Gerasimov said the “advance” into the Kursk region had been stopped, with Russian forces “continuing to destroy the adversary in areas directly adjacent to the Russian-Ukrainian border”.

Mr Gerasimov said Ukrainian forces aimed to take over the area around the town of Sudzha, and that Russia had already killed 100 men and injured another 215.

However, some popular and generally well-informed pro-war Telegram channels suggested the situation on the ground was not as stable as the Kremlin said.

Blogger Yuri Kotenok described the battles taking place in Sudzha and nearby Korenevo as “heavy”, while the channel Rybar said that the situation in the area around Sudzha was “continuing to deteriorate” and Ukrainian formations were advancing towards the town. The BBC is unable to verify these claims.

The Russian National Guard said it had strengthened the security of the Kursk nuclear power plant, which lies some 70km (43 miles) north-east of Sudzha.

In the Belgorod region, which neighbours Kursk, Governor Vyacheslav Gladkov also issued missile attack warnings throughout Tuesday and said several people had been injured in Ukrainian air attacks.

On Wednesday, the head of the Ukrainian region of Sumy, Volodymyr Artyukh, ordered the evacuation of the areas that border Kursk.

One colonel in Ukraine’s military, Vladislav Seleznyov, told the prominent Nexta channel the attack was “preventative”, with an estimated 75,000 Russian troops continuing to gather close to the border.

After a major cross-border incursion by Russia into the north-eastern Kharkiv region in May, there had been fears Moscow would attempt the same into the Sumy region further north.

With Ukraine now apparently capturing several settlements and highways the other way, those ambitions may well have been frustrated for now.

But with Ukrainian forces already overstretched and outmanned, some military analysts are questioning the wisdom of such cross-border raids.

This is not the first incursion into Russia by fighters based in Ukraine. Some groups of anti-Kremlin Russians launched raids last year, which were repelled.

The forces crossed into the Belgorod and Kursk regions again in March, where they engaged in clashes with Russian security forces.