Moscow's defence ministry said it had rushed its own troops and aviation units to the border in southwestern Kursk region after a morning raid by Ukrainian units -- the latest such cross-border attack throughout the conflict.

"Today the enemy made another attempt to break through into the territory of the Kursk region," Russia's defence ministry said in a statement on Tuesday evening.

"The enemy is being hit with artillery fire, strikes by army aviation units and attack drones," it added.

In a statement on its official Telegram channel at around 18:20 in Moscow (1520 GMT), the ministry initially said it had pushed the Ukrainian fighters out of Russian territory and that fighting inside Russia was over.

But it later edited that post, removing that claim and changing the wording to imply fighting was ongoing.

Earlier in the day Moscow despatched reserve forces to the border zone to defend against a Ukrainian group it said consisted of around 300 troops, 11 tanks and more than 20 armoured combat vehicles.

It published videos purporting to show Ukrainian tanks being hit from the air and said it had inflicted significant damage.

Footage on social media had earlier claimed to show Russian warplanes flying at low-altitude over the Kursk region as they battled to put down the attack.

The Russian governor of the region said three people had been killed throughout the day -- a woman in the attempted border incursion and two people whose vehicles were hit in separate drone attacks.

Several others were injured, including two children when a Ukrainian drone dropped an explosive device, governor Alexei Smirnov said.

In a video message to residents on Tuesday evening, Smirnov said the situation was "tense" but "under the control" of Russian forces.

"The situation in the border area continues to be tense. The Russian defence ministry and border guards are working. Please remain calm," he said.

- 'Cynical shelling' -

The Kursk region sits just across from Ukraine's northeastern Sumy region.

Ukraine did not comment on the reports but the head of the Sumy region military administration, Oleksiy Drozdenko, told residents to pay attention to air raid alerts.

Sumy regional authorities also said Ukrainian forces had shot down a Russian helicopter. Images on social media showed what independent military analysts said looked like a downed Russian KA-52 attack helicopter.

Ukrainian forces said there was "cynical shelling" of border settlements in the Sumy and neighbouring Chernigiv regions.

Combatants from Ukraine have made several brief incursions into Russia since the beginning of the conflict, including by units of Russians fighting in support of Kyiv -- the Russian Volunteer Corps and the Freedom of Russia Legion.

The latest attack comes almost three months after Russian President Vladimir Putin launched a major new offensive into northeastern Ukraine, a move he said was to create a security buffer to protect Russian border regions from shelling and aerial attacks.

That offensive was focused on Ukraine's Kharkiv region, to the southeast of the Sumy region, from where Tuesday's cross-border raid was mounted.

- Village seized -

Russian authorities also said Tuesday that Ukrainian "saboteurs" had attempted a landing by sea on the Russian-held Tendra Spit in southern Ukraine.

"According to preliminary information, 12 high-speed craft were used -- eight of them with the saboteurs and four with fire support," Moscow-appointed governor Vladimir Saldo said on social media.

"Russian marines opened fire as the boats were approaching the Tendra Spit. Three boats were destroyed with their crews and sank. The others turned back," Saldo said.

Meanwhile, Russia's defence ministry said its forces had captured another village in eastern Ukraine, the latest in a series of gradual advances in recent weeks.

Russian units "liberated the settlement of Timofeevka," it said on social media, using the Russian name for the village, which is known as Timofiyivka in Ukrainian.

Earlier in the day, the head of Russia's General Staff, Valery Gerasimov, had visited troop positions in occupied parts of Ukraine's eastern Donetsk region, the defence ministry said.

The general "heard reports from the commanders of units ... summed up his conclusions and set tasks for future actions", the ministry said, posting video of Gerasimov meeting soldiers in underground locations.