Drones targeted Russia's border region of Belgorod where security operations pressed into a second day after a cross-border infiltration by a Ukrainian sabotage group, authorities said Tuesday.

The region, which borders Ukraine, has been repeatedly shelled in attacks that have killed dozens of people since the start of the war in Ukraine last year.

Several drones struck houses and a government building overnight but did not result in casualties or deaths, Vyacheslav Gladkov, Belgorod governor, wrote on Telegram.

On Monday, Gladkov confirmed that a Ukrainian sabotage and reconnaissance group infiltrated the territory of the Grayvoronsky district of Russia's Belgorod region, adding that "the armed forces of Russia, together with the border service, the Russian Guard and the FSB, are taking the necessary measures to eliminate the enemy."

Russia said its troops were battling the sabotage group that entered from Ukraine and introduced an anti-terror regime in Belgorod.

Gladkov said on Tuesday the "defense ministry and law enforcement are continuing to clear the area."

The Belgorod governor previously said eight people had been injured, adding that authorities were helping people leave the scene of the fighting.

He added on Tuesday that it was too soon for residents who fled to return to their homes and said that authorities would give the all-clear when it was safe.

Members of the anti-Kremlin so-called "Freedom of Russia Legion" have claimed responsibility for the infiltration into Belgorod.

Ukrainian presidential advisor Mikhaylo Podolyak suggested on Monday that Russian "guerrilla groups" could be responsible.

Russia opens 'terror' probe over border incursion: Official

Russia said Tuesday it had launched a "terror" probe after Moscow's troops had been fighting a sabotage group that crossed from Ukraine.

"A criminal case has been opened over an attack on settlements in the Belgorod region," the Investigative Committee, which probes major cases, said in a statement.

Investigators said they opened a probe into a number of crimes including a "terror attack", attempted murder, destruction of or damage to property, and illegal circulation of weapons and explosives.

The statement said representatives of armed Ukrainian groups attacked the district of Graivoron in the southern region of Belgorod. 

"Residential and administrative buildings and civilian infrastructure facilities came under mortar and artillery fire," the Investigative Committee said.

"Several civilians were injured as a result of these criminal acts."

The attack on Russia's region was reported ahead of a widely expected Ukrainian spring offensive, though Ukrainian President Volodymyr Zelensky has said his country is not yet ready.

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