Russia on Friday declared a federal state of emergency in the Kursk region, where clashes with Ukrainian troops have raged for four days. 

The Emergency Ministry announced the decision following a meeting of the government commission for the prevention and elimination of emergency situations.

"The discussion included the situation in the Kursk region due to the attack by Ukrainian armed forces. A federal response level has been established in the region," the statement read.

Overnight Monday to Tuesday, Ukraine intensified shelling of the Kursk region. The artillery barrage was followed by an incursion of Ukrainian infantry, supported by tanks and armored vehicles, near the city of Sudzha.

The Russian Defense Ministry initially reported on Tuesday that 300 Ukrainian troops, 11 tanks, and 20 armored vehicles had crossed the Russian border. But on Wednesday, Russian Chief of General Staff Valery Gerasimov claimed that around 1,000 Ukrainian servicemen were involved in the battle.

Experts suggest several possible objectives for the assault, including the destruction of the Sudzha gas station – through which Russia pumps gas to Europe – diverting Russian command attention from Donbas, disrupting the railway supply route to Russian forces in Ukraine's Kharkiv region, and boosting the morale of the Ukrainian army.

Russian authorities also expressed concern for the Kursk nuclear power plant, located near the fighting, and have reportedly tightened security, according to the Russian Guard Corps.

Local authorities in the Kursk region reported that five civilians, including a paramedic, an ambulance driver, and a 24-year-old pregnant woman, were killed, and 66 others, including six children, were injured in Ukraine's attack. A major evacuation of several thousand people has been ordered from the combat zone.