Drones struck Russia's border region of Belgorod where security operations pressed into a second day after a cross-border raid blamed on fighters from Ukraine, authorities said Tuesday.

The region, which borders Ukraine, has been repeatedly shelled in attacks that have killed dozens of people since Moscow launched its offensive 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, Russia said its troops were battling a "sabotage" group that entered from Ukraine and introduced an "anti-terror regime" in Belgorod, a first since the start of Moscow's campaign in Ukraine in February 2022.

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

He 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 Freedom of Russia Legion have claimed responsibility for the incursion into Belgorod, but Kyiv has denied any involvement.

In a video released by a Telegram channel claiming to represent the group, a camouflaged spokesman, surrounded by armed men in fatigues, said: "Russia will be free!" -- a slogan frequently used by Russian opposition activists.

- 'Guerrilla groups' -

"We want our children to grow up in peace and be free," the spokesman added, with the channel claiming that two settlements including Graivoron had been attacked.

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

"The only driving political force in a totalitarian country of tightened screws is always an armed guerrilla movement," he said on Monday.

The "anti-terror regime" introduced in the southern region gives special powers to security services and entails the enforcement of a number of restrictions and measures including beefed-up security and communications surveillance. 

A similar regime was in place in Chechnya between 1999 and 2009, when Russian authorities battled insurgents during Moscow's second military campaign in the mountainous region.

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

The timing and focus of Ukraine's offensive have been the subject of months of speculation, while Kyiv has said almost nothing except that it needs more weapons from its backers.

At the same time, Russia has been reinforcing hundreds of kilometres of front line with tank barriers, trenches and troops.

Given that the battles would come after a significant influx of Western armaments, success or failure could undermine future support or increase pressure on Kyiv to negotiate.

bur/jm/giv