Russian President Vladimir Putin quipped on Friday that in his view the whole of Ukraine was "ours" and cautioned that advancing Russian forces could take the Ukrainian city of Sumy as part of a bid to carve out a buffer zone along the border.

Putin, who ordered troops into Ukraine in 2022 after eight years of fighting in eastern Ukraine, also said he was not seeking the capitulation of Ukraine or denying Ukraine's sovereignty, but that Ukraine had to be neutral.

Russia currently controls about a fifth of Ukraine, including Crimea, more than 99% of the Luhansk region, over 70% of the Donetsk, Zaporizhzhia and Kherson regions, and fragments of the Kharkiv, Sumy and Dnipropetrovsk regions.

Asked about fresh Russian advances, Putin told the St Petersburg International Economic Forum that he considered Russians and Ukrainians to be one people and "in that sense the whole of Ukraine is ours".

Kyiv and its Western allies say Moscow's claims to four Ukrainian regions and Crimea are illegal, and Ukrainian President Volodymyr Zelenskyy has repeatedly rejected the notion that Russians and Ukrainians are one people.

He has also said that Putin's terms for peace are akin to capitulation.

Putin said on Friday he was not questioning Ukraine's independence or its people's striving for sovereignty, but he underscored that when Ukraine declared independence as the Soviet Union fell in 1991 it had also declared its neutrality.

Putin said Moscow wanted Ukraine to accept the reality on the ground if there was to be a chance of peace - Russia's shorthand for the reality of Russia's control over a chunk of Ukrainian territory bigger than the U.S. state of Virginia.

"We have a saying, or a parable," Putin said. "Where the foot of a Russian soldier steps, that is ours."

Putin said Russian forces were carving out a buffer zone in Ukraine's Sumy region in order to protect Russian territory and said he did not rule out those same troops taking control of the regional capital of Sumy.

The depth of the zone under Russian control in the Sumy region was 8-12 km, Putin said.

"Next is the city of Sumy, the regional center. We don't have the task of taking it, but in principle I don't rule it out," he said.