Ukraine said on Wednesday its forces had advanced further into Russia's Kursk region in the biggest foreign incursion into Russia since World War Two, posing a dilemma for President Vladimir Putin according to U.S. President Joe Biden, Paralel.Az reports citing Reuters.

Thousands of Ukrainian troops rammed through the Russian border in the early hours of Aug. 6 into Russia's western Kursk region in what Putin called a major provocation aimed at gaining a stronger hand in possible future ceasefire talks.

Ukraine has carved out a slice of the Russian border region of Kursk and though Putin said the Russian army would push out the Ukrainian troops, more than a week of intense battles have so far failed to oust them.

Ukrainian President Volodymyr Zelenskyy said Kyiv's forces were continuing to gain ground in the Kursk region and that they had taken another one to two kilometres on Wednesday.

"We continue to advance further in the Kursk region," Zelenskyy wrote in a statement on Telegram, "from one to two kilometres in various areas since the start of the day. And more than 100 Russian prisoners of war in the same period."

Russia's defence ministry said 117 Ukrainian drones had been shot down within its territory overnight, mostly in the Kursk, Voronezh, Belgorod and Nizhny Novgorod regions. It said missiles had also been downed, and showed Sukhoi Su-34 bombers striking Ukrainian positions in the Kursk region.

Later, the ministry said Russian forces had repelled a series of Ukrainian attacks inside the Kursk region, including at Russkoye Porechnoye 18 km (11 miles) from the border, and pro-Russian war bloggers said the front has been stabilised.

The Ukrainian drone attack included strikes on four Russian military airfields in an attempt to undermine Russia's ability to attack Ukraine with gliding bombs, a Ukrainian security source told Reuters on condition of anonymity.

Russia's National Guard said it was beefing up security at the Kursk nuclear power plant, located just 35 km (22 miles) from the fighting.