Russia said on Wednesday it was fighting intense battles against Ukrainian forces that had penetrated its southern border near a major natural gas transmission hub, in one of the largest incursions into Russian territory since the war began.
The acting governor of Kursk region, Alexey Smirnov, said he had introduced a state of emergency in the border region. Regional officials said that meant restricting access to specific areas.
Russia's health ministry said 31 civilians, including six children, had been wounded. Smirnov said on Tuesday that five people had been killed.
No information on military casualties was available.
Russia's National Guard said it had beefed up security around the nearby Kursk nuclear power station and its four reactors.
Russia has advanced this year after the failure of Ukraine's 2023 counteroffensive to achieve major gains, and has taken 420 square km (162 square miles) of territory from Ukrainian forces since June 14, Russian officials say.
Ukraine struck back on Tuesday, and battles continued through the night into Wednesday as Ukrainian forces pushed to the northwest of the border town of Sudzha, 530 km (330 miles) southwest of Moscow, Russia's defence ministry said.
"The Kyiv regime has launched another major provocation," President Vladimir Putin told members of the Russian government, referring to the attack in Kursk region.
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