Moscow's troops have been engaged in a concerted push into the region, raising alarm among Ukrainians and their Western allies that a large-scale assault on the major city of Kharkiv is coming.

Kharkiv city, the second-largest in Ukraine, is located just 30 kilometres south of the Russian border.

"The enemy is currently achieving tactical success," the Ukrainian General Staff said in its situation report posted on social media early Monday morning.

Following the capture of several villages in the predominantly Russian-speaking Kharkiv region, fighting is currently underway around the city of Vovchansk, only 5 kilometres from the Russian border, the General Staff of the Ukrainian Armed Forces said.

Despite incurring heavy losses, Ukraine said the Russian military is deploying significant forces in the battle for Vovchansk, with up to five battalions bearing down on the city.

Vovchansk had come under Russian occupation at the beginning of the war. During Ukraine's autumn offensive in 2022 in the Kharkiv region, Russian troops withdrew from Vovchansk. According to Ukrainian figures, around 3,500 people were still living in the city at the time.

Russia launched a renewed campaign in the Kharkiv region on May 10. Over the past two days, the Russian Defence Ministry has reported the capture of nine villages.