Russia is claiming its forces have entered the north-eastern border town of Vovchansk, near Ukraine's second-largest city, Kharkiv.
Ukraine says there is still heavy fighting taking place there.
Russia has intensified its attacks on the region following a surprise incursion across the border on May 10, seizing several villages in one of the most significant ground attacks since its full-scale invasion of Ukraine in February 2022.
Ukraine is on the defensive after months of slowed supplies of U.S. munitions. Russia's forces hold a significant advantage in manpower and munitions.
In 2022, soon after the start of their full-scale invasion, Russian forces reached the suburbs of the city of Kharkiv before being driven back to the border.
