Russia has sent reinforcements – including tanks and missile launchers – to the Kursk region

The country has imposed a "counter-terrorist operation" regime in three regions to try to stop a sudden cross-border incursion by Ukrainian troops.

Authorities in Kursk, Belgorod and Bryansk regions on the border with Ukraine can now restrict the movement of people and vehicles and use wiretapping, among other measures.

This is happening after five days of the Ukrainian offensive in the Kursk region, "BBC" reports.

Reports say Ukrainian troops are threatening to capture a regional town as they fight their way more than 10 kilometers into Russia – the deepest advance since Moscow launched its full-scale invasion of Ukraine in February 2022.

Russia must feel the consequences of the war, Zelensky said after the start of the Ukrainian attack.

The new security measures in the three Russian border regions were announced by the National Anti-Terrorism Committee yesterday.

It said this was done "to ensure the safety of citizens and suppress the threat of terrorist acts by enemy sabotage and reconnaissance units."

Authorities now have powers to enter private homes, restrict the movement of traffic and pedestrians, order the temporary relocation of people and monitor information sent electronically.

This comes as Moscow struggles to contain the Ukrainian offensive.

Russian state news agency Tass said more than 76.000 people have already been evacuated from the border areas of the Kursk region.

Russia claims up to 1.000 Ukrainian troops, backed by tanks and armored vehicles, entered the Kursk region on Tuesday morning.

Since then, the Ukrainians have reportedly captured a number of villages and are also threatening the regional town of Suja.

A video emerged on Friday purportedly showing armed Ukrainian soldiers claiming to be in control of the city, as well as a key Russian gas facility there owned by the Gazprom company.

"BBC" confirmed that the footage is indeed from the Gazprom facility in the north-western outskirts of Sudja, about 7 kilometers from the border with Ukraine.

But the video does not confirm the position of the Ukrainian soldiers that they captured the entire city.

Russian military bloggers previously claimed that the city was in Moscow's hands.

In its latest report this morning, Russia's Defense Ministry said its troops "continue to repel an invasion attempt" by Ukrainian forces.

It claims that Ukraine's attempts to "penetrate deep into Russian territory" have been thwarted.

The Russian claims have not been independently verified.

On Friday, the UN nuclear agency called on Russia and Ukraine to "exercise maximum restraint" as fighting nears the Kursk nuclear power plant - one of Russia's largest such facilities.

The head of the International Atomic Energy Agency, Rafael Grossi, said measures must be taken "to avoid a nuclear accident with potentially serious radiological consequences".

The power plant is located about 60 kilometers north-east of Suja.