Ukrainian presidential adviser Mykhailo Podolyak says Ukraine is not interested in occupying the territory it has captured in Russia's western region of Kursk but wants to form a "security belt" to thwart Russian attacks.

Ukraine claims it has taken control of 1,150 square kilometers of Russian territory since it launched a cross-border attack into Kursk on August 6.

Podolyak said on social media on Thursday that Ukraine's intent is to push back Russian troops to prevent artillery and missile strikes from reaching Ukrainian territory.

Podolyak also said Ukraine aims to destroy Russia's military logistics and infrastructure. He stressed that the nature of the incursion was different from Russia's invasion and was a "defensive war" to ensure the protection of its population.

British newspaper the Financial Times quoted Ukraine's military intelligence as saying that it was negotiating a prisoner exchange with Russia.

The Russian defense ministry posted a video on Wednesday showing what it claimed were Ukrainian soldiers captured in Kursk.

Meanwhile, Kyiv said Ukrainian forces took more than 100 Russian troops prisoner on Wednesday.

The head of the Security Service of Ukraine, Vasyl Maliuk, said Kyiv is thinking of how to make the most of the captives to bring home their own fighters held by Russia.