Ukraine kept pounding the Russian border region of Kursk with missiles and drones on Wednesday, as Kyiv said it had made further territorial gains in an incursion that U.S. President Joe Biden called a "real dilemma" for the Kremlin's leader.

Four Ukraine-launched missiles were destroyed over Kursk and the whole region was under air raid alerts on and off most of the night, its regional acting governor said early Wednesday.

Kyiv said on Tuesday it had taken control of 74 settlements in Kursk, a week after thousands of Ukrainian soldiers launched a startling attack through the Russian border.

Ukraine's account was jarred with Russia's assertions that Kyiv's troops had been halted and attacks had been repelled at villages about 26 to 28 km (16 to 17 miles) from the border.

Reuters was not able to independently verify the battlefield situation.

Russian President Vladimir Putin said the attack was aimed at improving Kyiv's negotiating position ahead of possible talks and slowing Russia's frontline advance.

The incursion has suddenly shifted the dynamics of the war, which Moscow started with its full-scale invasion on Ukraine in 2022, giving President Volodymyr Zelenskiy first significant gains after months of Moscow's steady territorial advances in Ukraine.

Biden, in his first substantive comments, said Washington is in constant contact with Kyiv about the operation, although the White House said earlier it was not engaged in any aspect of planning or preparation.

"It's creating a real dilemma for Putin," Biden said.

A Russian military blogger close to the defence ministry who goes by the name "Rybar" said on the Telegram messaging app that Ukrainian forces were attacking in several areas at once. Russian troops were "pinning down" Kyiv soldiers, striking their armoury, while reinforcements were arriving.

Kursk's acting governor, Alexei Smirnov, said on Telegram that Russian soldiers were "fighting shoulder to shoulder" for victory.

  - Reuters