The acting governor of the Kursk region, Alexey Smirnov, said he had declared a state of emergency in the border region, but it was not immediately clear what measures had been taken.

The Russian health ministry said 31 civilians, including six children, were injured. No information was given about military casualties.

The Russian National Guard said it has strengthened security around the Kursk nuclear power plant and its four reactors.

Russia has made progress this year after Ukraine's counteroffensive in 2023 failed to achieve any major results and has captured 420 square ^kilometers of territory from Ukrainian forces since June 14.

Ukraine counterattacked on Tuesday and fighting continued overnight into Wednesday as Ukrainian forces advanced northwest of the border town of Sudzha, 530 km southwest of Moscow.

Commenting on the attack in Kursk, Russian President Vladimir Putin said in front of the Russian government: "The Kyiv government has committed a serious provocation."

Chief of the General Staff Valery Gerasimov told President Putin that Russian forces had thwarted an attack by a group of 1,000 Ukrainian soldiers – three times the number given by the Russian Defense Ministry on Tuesday – and would push them back from the border.

"The enemy group's advance into the territory at Kursk was stopped by the actions of the state border protection units together with the border guard and reinforcement units. Russian forces deployed air, missile and artillery strikes," Gerasimov said in televised comments.

The Ukrainian military appears to have adopted a strategy of complete silence.

President Volodymyr Zelenskiy made no mention of the attack in his evening video address on Wednesday, continuing to encourage Kyiv troops to fight and weaken Russian forces.

The Ukrainian General Staff also did not mention the attack in its daily battlefield update, but said Russia had stepped up its use of warplanes in the Sumy region on the border between the two countries.

In Washington, US State Department spokesman Matthew Miller said the US had been in contact with Ukrainian authorities about the actions in the Kursk region.

He insisted that US rules governing how Ukraine uses weapons it has provided – particularly around the Russian border – still apply, and that Ukraine’s actions “cannot be considered a violation of that policy.”

Gas transportation system

Fighting has broken out around Sudzha, the only operational transit point for Russian gas to Europe via Ukraine. The Urengoy–Pomary–Uzhhorod pipeline is expected to transport around 14.65 billion ^cubic metres of gas in 2023, about half of Russia’s gas exports to Europe.

Ukraine’s gas transit company said Russian natural gas was still being transported to European consumers as normal. The Kursk nuclear power station is just 60 km northeast of Sudzha.

The fighting in Sudzha comes at a crucial juncture in the conflict. Ukraine is losing territory and Kyiv fears that US support could wane if Donald Trump wins the November 2024 presidential election.

Mr Trump has vowed to end the war, so both Russia and Ukraine want to be in the best negotiating position on the battlefield. Ukraine wants to deter Russian forces and show the West that it can still fight big battles.

Tensions at Kursk

Russian military bloggers have described the situation in Kursk as more dire than officials have reported, with some suggesting that Ukraine has opened a new front. Russia has called up reservists to bolster its defenses in the region.

Some bloggers have suggested that Ukraine may be planning to move towards the Kursk nuclear power station.

Russia has inflicted heavy casualties on the Ukrainian attack group in terms of manpower and material, Gerasimov said, giving some figures that Reuters could not verify.

President Putin affirmed that Ukrainian forces had "indiscriminately" attacked a number of civilian targets in the area.

Kyiv and Moscow both deny targeting civilians in the war.

Telegram channels from Russia have posted several unverified videos of several homes being bombarded.

Forces calling themselves pro-Ukrainian volunteer militias have infiltrated several areas in the Kursk and Belgorod regions this year, after Russian troops established a buffer zone in northeastern Ukraine.

Nguyen Quang Minh (according to Reuters)