Ukrainian President Volodymyr Zelensky confirmed on Monday for the first time that Ukrainian military forces are operating within Russia’s Kursk region. Zelensky made this statement in a post on Telegram, praising the country's soldiers and their leaders "for their resilience and decisive actions."

He did not provide further details regarding the military incursion.

He suggested that Ukraine is offering humanitarian aid in the region, stating that government officials have been instructed to prepare a humanitarian plan for the area.

Russian President Vladimir Putin stated on Monday that the Ukrainian army's incursion into the Kursk region, which has caused over 100,000 civilians to flee and embarrassed the Kremlin, is an attempt by Kyiv to halt Moscow's offensive in the Donbas area of eastern Ukraine and to gain leverage in potential future peace talks.

Russian forces are still rushing to respond to the sudden Ukrainian attack after nearly a week of heavy fighting, but Putin insisted that Moscow's army would prevail.

Speaking at a meeting with senior security and defense officials, Putin said that the attack, which started on August 6, seems to reflect Kyiv's attempt to gain a better negotiating position in potential future talks to end the war.

He said that Ukraine may have hoped the attack would cause public disturbances in Russia, but it failed to achieve that goal, claiming that the number of volunteers joining the Russian army has increased due to the attack. He stated that Russian forces would continue their offensive in eastern Ukraine regardless.

Putin said, "It is clear that the enemy will continue to try to destabilize the situation in the border area to attempt to destabilize the internal political situation in our country." He added that Russia's main task is to "pressure the enemy and drive them out of our territories, and in cooperation with the border service, to ensure reliable coverage of the state border."

Acting Governor of Kursk Alexey Smirnov reported to Putin that Ukrainian forces had invaded 12 kilometers (7.5 miles) into the Kursk region along a front of 40 kilometers (25 miles) and currently control 28 Russian settlements.

Smirnov stated that 12 civilians have been killed and another 121 injured, including 10 children, in the operation. He added that around 121,000 people have been evacuated or have left the fighting-affected areas on their own. The total number of planned evacuations is 180,000 people.

Smirnov said that tracking all Ukrainian units roaming the area and creating detours is difficult, noting that some are using fake Russian identification cards.

The governor of neighboring Belgorod region has also announced the evacuation of people from an area near the Ukrainian border.

Ukrainian forces quickly infiltrated the town of Sudzha, located about 10 kilometers (six miles) across the border after launching the attack. They are reportedly still controlling the western part of the town, which is the site of an important natural gas station.

The Ukrainian operation is under strict secrecy, and its objectives remain unclear, especially whether Kyiv's forces intend to hold territory or conduct raid-like attacks. The stunning maneuver that caught Kremlin forces off-guard contrasts with Russia's ongoing efforts in recent months to breach Ukrainian defenses at selected points along the front line in eastern Ukraine.

Russia has witnessed previous incursions into its territory during the nearly two-and-a-half-year war, but the incursion into the Kursk region marks the largest attack on its land since World War II, representing a significant milestone in hostilities. This is also the first time the Ukrainian army has led an invasion rather than Russian fighters loyal to Ukraine.

The advance has dealt a blow to Putin's efforts to pretend that life in Russia has not been significantly affected by the war. Government propaganda has tried to downplay the attack, emphasizing the authorities' efforts to assist residents of the region and seeking to divert attention from the army's failure to prepare for and quickly repel the attack.

Residents of Kursk recorded videos lamenting their need to flee the border area, leaving their belongings behind, and pleading with Putin for help. But state-controlled media in Russia imposed a tight lid on any expression of discontent.

Retired General Andrei Gurulev, a member of the State Duma in the Russian parliament, criticized the army for failing to protect the border properly.

He said on his messaging app channel: "Unfortunately, the group of forces protecting the border did not have its own intelligence assets. No one likes to see the truth in reports; everyone just wants to hear that everything is fine."

The fighting inside Russia has raised questions about whether Ukraine is using weapons provided by NATO member countries. Some Western nations have refrained from allowing Ukraine to use its military aid to strike Russian territory, fearing it could escalate tensions that might drag Russia and NATO into war.

While it is not clear what weapons Ukraine is using across the border, Russian media widely reported that American-made Bradley armored vehicles and German-made Marder vehicles were present. This claim could not be independently verified.

Ukraine has already used American weapons to strike inside Russia.

Italian Foreign Minister Antonio Tajani said in an interview published on Monday that the weapons supplied by his country "cannot be used to attack Russia on its territory."

Meanwhile, German Defense Ministry spokesman Arne Collatz said on Monday that legal experts agree that "international law states that a state defending itself may also defend itself on the territory of the aggressor. This is clear from our perspective as well."

The Russian Defense Ministry announced on Monday that reinforcements sent to the region, supported by air and artillery forces, repelled seven attacks launched by Ukrainian units near Martinovka, Burki, and Korinovo over the past 24 hours.

The ministry stated that Russian forces also prevented an attempt by mobile Ukrainian groups to advance deep into Russian territory near Kayushok.

It added that Russian air and artillery also struck concentrations of Ukrainian troops and equipment near Sudzha, Korilovka, Bekhovo, Lyubimovo, and several other settlements. The ministry noted that warplanes and artillery hit Kyiv's reserves in the Ukrainian Sumy region across the border.

Basi Barvinen, an analyst at the Finland-based open-source intelligence agency Black Bird Group, which monitors the war, said the toughest phase of the Ukrainian incursion is likely to begin now with Russian reserves entering the battle.