KYIV, Aug 13 - Ukraine said on Tuesday its biggest cross-border assault of the war to date had taken control of 74 settlements in Russia's region of Kursk and was still advancing, making gains of one to three km in the last 24 hours, Reuters reported.

Ukraine blindsided Moscow by pouring thousands of troops into the western Russian region of Kursk last week. The surprise operation has given Ukraine its biggest battlefield gains since 2022 after months on the backfoot.

Kyiv's account jarred with the picture painted by Russia where Major General Apti Alaudinov said Ukraine's troops had been halted, while the defence ministry said attacks had been repelled at villages about 26 to 28 km (16 to 17 miles) from the border.

President Volodymyr Zelenskiy said Kyiv's forces had rounded up Russian prisoners of war who could be swapped for captured Ukrainian fighters, touting what he described as an expanding "exchange fund".

"Despite difficult and intense battles, our forces continue to advance in the Kursk region, and our state's 'exchange fund' is growing. Seventy-four settlements are under Ukrainian control," Zelenskiy said.

Shown speaking by video link, the Ukrainian leader asked his top commander, Oleksandr Syrskyi, to develop the next "key steps" in the operation.

"Everything is being executed according to the plan," Syrskyi replied, without elaborating.

Kyiv has disclosed few details about its plans, in stark contrast with last year's counteroffensive that was vaunted for months in advance and which ended up failing to breach well-prepared Russian defensive lines.

A week after the start of the shock offensive, Kursk regional governor Alexei Smirnov called on residents to show patience and character.

"I'll say it straight: the crisis has not yet been overcome," he wrote on social media.

Russian President Vladimir Putin has vowed to hit back at Ukraine with a "worthy response" and accused Kyiv's "Western masters" of helping Ukraine.

At the United Nations, Russia called out Kyiv's allies for not condemning the incursion.

U.S. President Joe 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.

Ukraine has cast the operation as defensive, saying its troops have taken control of areas Russia has used to launch more than 2,000 cross-border strikes since June.

"Ukraine is not interested in taking the territory of the Kursk region, but we want to protect the lives of our people," foreign ministry's spokesman Heorhii Tykhyi said.

Russian forces have been trying to advance for months on multiple fronts in the eastern Donetsk region, taking advantage of their greater troop numbers to inch towards cities like the Kyiv-held logistics hub of Pokrovsk. (rt/ez)