Russia has launched a counter-attack in the Kursk border region where Ukrainian forces last month launched a surprise cross-border incursion.

“The Russians have started counteroffensive actions,” Ukrainian President Volodymyr Zelensky said during a news conference Thursday, his first comments since reports emerged of Russia fighting back in Kursk.

Ukraine has been anticipating a Russian reaction and a counteroffensive is in line with the ‘Ukrainian plan,’ Zelensky said.

Zelensky has previously said that the surprise attack on Russia’s Kursk region was the initial step in a four-part “victory plan.”

The Russian Ministry of Defense said in a statement Thursday that Russian forces had “penetrated” into the Kursk region, capturing 10 settlements.

A social media video geolocated by CNN showed a Russian mechanized assault group in the settlement of Snagost on the western edge of territory controlled by Ukraine.

On August 6, Ukrainian forces stormed into the Kursk region in a shock, lightning strike that caught even American officials by surprise. It marked the first foreign attack on Russian soil since World War Two and saw thousands of troops burst through the border into the region armed with heavy weaponry.

It signaled that, despite Russia’s advantage in terms of men and armor, its military has vulnerabilities.

The attack left Russia scrambling to shore up its defenses, with US officials telling CNN that Moscow had to divert thousands of troops from occupied territory inside Ukraine to counter the threat. Russian President Vladimir Putin was forced to bring in conscripts, backpeddling on a promise he made not to use them on the frontline.

Last week, Zelensky said Ukraine had captured around 100 settlements in the Kursk region, and around 1,300 square kilometers (500 square miles) of territory.

One aim of the incursion was to divert Russian forces away from the eastern frontline in Ukraine, where they continue to make incremental gains. Another apparent goal was to boost morale in the Ukrainian army after a torrid few months.

Experts told CNN that Ukraine’s bold gambit to breach Russia’s border – planned in total secrecy – had stunned even Kyiv’s closest allies and shifted the playing field of a more than two-year war.

In a joint public appearance on Sunday, both CIA chief Bill Burns and Head of MI6 Richard Moore endorsed Ukraine’s invasion of Kursk, with Moore saying that it changed the narrative, and Burns that it was a significant tactical achievement.

Red Cross workers killed

In a separate development, Russian shelling killed three employees of the International Committee of the Red Cross (ICRC) while they were working in eastern Ukraine, Zelensky said.

The ICRC said its workers were killed when their vehicles were hit as they prepared to distribute wood and coal briquettes to residents in the region.

The organization did not say who was behind the shelling.

”We are shattered,” ICRC Ukraine Spokesman Pat Griffith told CNN. “Three of my colleagues killed, two injured, during an aid distribution in Donetsk region.”

The three ICRC staffers who were killed in the artillery shelling were Ukrainian nationals, Ukraine’s Ombudsman Dmytro Lubinets said.

ICRC teams are regularly present in the Donetsk region and their vehicles are “clearly marked with the Red Cross emblem,” the organization said.

The ICRC called for the respect of international humanitarian law, “including by taking every precaution possible to ensure that those engaged in humanitarian activities are not targeted or caught in hostilities.”