Russia's military says it has recaptured almost all areas of the country's Kursk region previously seized by Ukrainian forces.



The military says that its troops have retaken control of more than 86 percent of the areas occupied by the Ukrainians in the western Russian region.



Russian President Vladimir Putin said on Thursday that Kursk is under Russia's control, and Ukrainian troops that invaded the Russian territory are isolated.



The Russian forces are now apparently trying to advance into the northeastern Ukrainian region of Sumy, which borders Kursk.



Ukraine's 36th Separate Marine Brigade posted an update, along with a video, on social media on Thursday saying it had eliminated Russian and North Korean combat units traveling on four-wheeled vehicles in the border area.



A spokesperson for Ukraine's border security authorities told reporters that Russian forces are trying to cross the border and establish a foothold in Ukrainian territory. The official added that the move is aimed at besieging Ukrainian troops in Kursk or cutting off their supply lines.



The US-based Institute for the Study of War cited Russian military bloggers in its assessment on Thursday.



The bloggers say Russian forces may launch a coordinated offensive into the Sumy region in the coming weeks and months. There are concerns that fighting could intensify in the border areas.