Ukrainian troops have advanced up to 10 kilometers into Russia, possibly the most serious border incursion in the conflict, the Institute for the Study of War announced today.

Pro-Kiev forces stormed into Russia's southwestern Kursk region on Tuesday morning, deploying about 1.000 troops and more than two dozen armored vehicles and tanks, according to the Russian army.

Kyiv has not officially commented on the operation.

Russia's top general vowed yesterday to halt the incursion and push Ukrainian fighters back to the border.

"Ukrainian forces have made a confirmed advance of up to 10 kilometers in Russia's Kursk region amid continued mechanized offensive operations on Russian territory. The current confirmed extent and location of Ukrainian advances in the Kursk region indicate that Ukrainian forces have penetrated at least two Russian defense lines and a stronghold," the US Institute for the Study of War said in its latest update.

The progress is centered on the logistics hub of Suja, a town of about 5.000 residents located eight kilometers from the Ukrainian border.