Ukrainian troops have advanced up to 30 kilometers into Russia, the deepest and most significant advance since Moscow began its large-scale invasion of Ukraine in February 2022.

The Russian Defense Ministry said its forces encountered Ukrainian troops near the villages of Tolpino and Obshchy Kolodez on the sixth day of the offensive in the Kursk region.

Foreign Ministry spokeswoman Maria Zakharova accused Kiev of “intimidating the peaceful population of Russia.”

President Volodymyr Zelensky, who directly confirmed the attack for the first time in a speech last night, said Russia had launched 2,000 cross-border attacks from Kursk this summer.

“Artillery, mortars, drones. We are also seeing rocket attacks, and each of these attacks deserves a fair response,” Zelensky said in his evening address to the country from Kyiv.

A senior Ukrainian official told AFP that thousands of soldiers were involved in the operation, far more than the small incursions initially reported by Russian border guards.

Although Ukrainian-backed sabotage groups have repeatedly carried out cross-border incursions, the Kursk Offensive is the largest coordinated attack by Kiev’s conventional forces on Russian territory.

“We are on the offensive. Our goal is to stretch the enemy’s positions, inflict maximum losses and destabilize the situation in Russia, since Russia is unable to protect its own border,” the official said.

The Russian Defense Ministry said on Sunday that its armed forces had “thwarted attempts by enemy mobile groups with armored vehicles to penetrate deep into Russian territory.”

However, the Defense Ministry apparently admitted that Kyiv’s forces had now advanced deep into the Kursk border region, reporting that there were clashes with Ukrainian troops near the villages of Tolpino and Obshchy Kolodez, which are about 25 and 30 kilometers from the Russian-Ukrainian border, respectively.

Footage circulating online and verified by the BBC also appeared to show a Russian attack near the village of Levshinka, about 25 kilometers from the border.

Ukrainian troops say they have captured several settlements in the Kursk region. In Guevo, a village about three kilometers inland in Russia, soldiers filmed themselves removing the Russian flag from an administrative building.

Footage has also emerged showing Ukrainian troops taking over administrative buildings in Sverdlikovo and Poros, while heavy fighting is reported in Sudzha, a town of about 5,000 inhabitants.

Ukrainian troops have already filmed themselves visiting a large gas plant outside Sudzha, which is part of the natural gas transit route from Russia via Ukraine to the EU, which has continued despite the war.

In the Sumy region, which borders the Kursk region, BBC reporters witnessed a steady stream of armoured personnel carriers and tanks moving towards Russia.

The tank convoys carry white triangular insignia that appear to distinguish them from the armor used in Ukraine. Meanwhile, aerial photographs appear to show Ukrainian tanks in combat on Russian territory.

Photos analyzed by BBC Verify also appeared to show Russia building new defense lines near the Kursk nuclear power plant. Ukrainian forces deployed in Obshchy Kolodets were 50 km from the plant.

Comparing satellite images of the same site taken yesterday and images taken a few days ago, several newly constructed trenches can be seen in the area, the nearest of which is about 8 km (5 miles) from the power plant.

According to Russia, 76,000 people were evacuated from the border areas of the Kursk region, where local authorities declared a state of emergency.

Acting regional governor Alexei Smirnov also said that 15 people were injured late Saturday night when the wreckage of a fired Ukrainian missile fell on a multi-storey building in the regional capital of Kursk.

Oleksiy Goncharenko, a Ukrainian MP, welcomed the operation, saying it “brings us much closer to peace than a hundred peace summits.”

“If Russia has to strike back on its own territory, if the Russian people are fleeing, if people care, then this is the only way to show them that this war must end,” he told the BBC.

The offensive on Kursk comes after weeks of Russian advances in the east, where Kremlin forces captured a number of villages.

Some analysts suspect that the attack on the Kursk was part of an effort to force Russia to withdraw troops from eastern Ukraine and thus relieve pressure on the beleaguered Ukrainian defense.

However, the Ukrainian official told AFP that there had been little easing of Russian operations in the east so far.

Earlier this week, Russian President Vladimir Putin described the offensive as a “major provocation.”

Meanwhile, emergency services in the Kyiv region said a man and his four-year-old son were killed in a rocket attack near the capital overnight.

Air defenses also destroyed 53 of 57 attack drones that Russia launched during its nighttime air strikes, air force officials said. Four North Korean-made missiles were also fired during the attack, they said.

Russia has been forced to turn to the isolated Asian state to replenish its ammunition stocks, while the US claims that Pyongyang has supplied large quantities of military equipment.

Elsewhere, Russian officials in the occupied Zaporizhia region said a fire broke out at the region’s nuclear power plant on Sunday.

Yevgeny Balitsky, the Kremlin-appointed governor of Zaporizhia, claimed the fire broke out after an attack by Ukrainian forces. He said there were no radiation spikes in the area around the power plant.

Russian state news agency Tass reported that the main fire at the plant was extinguished in the early hours of Monday.

In a statement published on X, the International Atomic Energy Agency (IAEA) said its on-site inspectors had observed “heavy, dark smoke” coming from the north of the plant. However, it stressed that “no impact” on nuclear safety had been reported.

President Zelensky said in a social media post that Russian forces had set fire to the plant’s premises.

The site has been under the control of Russian troops and officials since 2022. It has not produced electricity for more than two years and all six reactors have been in cold shutdown mode since April.

With additional reporting by Benedict Garman.