Ukraine warned Thursday that it faced a "very difficult" situation in its northeastern Kharkiv region, where Moscow has made its largest territorial gains in 18 months since launching a surprise offensive last week.As Ukrainian President Volodymyr Zelensky announced Kyiv was sending more reinforcements to the area, the Ukrainian army said it had managed to partially halt Russia's advance.Kyiv also accused Russian troops of executing civilians in territory it had captured over the last week.Moscow has seized 278 square kilometers of Ukrainian territory between May 9 and 15, according to AFP calculations based on data from the Institute for the Study of War, making it the largest territorial gain in a single operation since mid-December 2022.Ukraine President Volodymyr Zelensky on Thursday met military leaders in the city of Kharkiv, located some 30 kilometers from the Russian border, to assess Ukraine's defensive efforts."The situation in the Kharkiv region is generally under control, and our soldiers are inflicting significant losses on the occupier," he said in a post on social media.

"However, the area remains extremely difficult.

We are reinforcing our units."Ukraine's army said earlier it had managed to halt the advancing Russian forces in some places."Our defense forces have partially stabilized the situation.

The advance of the enemy in certain zones and localities has been halted," army spokesman Nazar Voloshin said on state television Thursday.In a daily briefing, Ukraine's General Staff said its forces had "significantly reduced the activity of the Russian occupiers.""But the enemy is still trying to create the conditions for further advances," Voloshin warned.