"More than 30 settlements in the Kharkiv region came under enemy artillery and mortar fire," regional governor Oleg Synegubov said on social media at midday.

According to the official, 5,762 residents have been evacuated from these areas since the fighting began. Another 1,600 people were due to leave on Monday, despite what he described as a "rather complicated situation".

Russian forces crossed the border on Friday to launch an offensive towards Lyptsi and Vovchansk, two towns located about 20 and 50 kilometres (12 and 30 miles) respectively northeast of Kharkiv, Ukraine's second-largest city.

"The enemy is currently having tactical successes," the Ukrainian general staff admitted on Monday, indicating that Moscow had deployed "up to five battalions".

According to the Telegram channel DeepState, which is close to the Ukrainian army, the Russians have managed to occupy a strip of about 70 square kilometres (27 square miles) in the Lyptsi area and another 34 square kilometres (13 square miles) towards Vovchansk.

Meanwhile, one person was killed and three others were injured in an attack on a farm in a village west of Kharkiv, about 30 kilometres (18 miles) from the combat zone, regional authorities said.

In the village of Ruski Tyshki, seven kilometres (four miles) from Lyptsi, explosions could be heard regularly in the distance, AFP journalists found.

According to the Telegram channel Rybar, which is close to the Russian army, after four days of offensive, "there has been no large-scale breakthrough of the enemy's defences".

After clearing the "grey" border area, Russian assault units have focused on "penetrating the strongholds and defensive lines of the Ukrainian armed forces", the same source said.

On Sunday evening, Ukrainian President Volodymyr Zelensky spoke of "defensive battles and fierce fighting (...) along a large part" of the border.

"The idea behind the attacks in the Kharkiv region is to stretch our forces and undermine the morale" of the Ukrainian military, he said.

The large city of Kharkiv is not under threat for the moment, "despite all the events that are taking place in the region", the city's mayor, Igor Terekhov, also said on Sunday.

"It is calm, we do not see people leaving," the mayor said.

Ukrainian authorities have been warning for weeks that Moscow could try to attack the northeastern border regions of Ukraine, a country that is currently facing delays in Western aid and a shortage of soldiers.

Russia's move comes as Russian President Vladimir Putin made a surprise shake-up in Moscow on Sunday evening, replacing his emblematic defence minister, Sergei Shoigu, after two years of conflict in Ukraine with no clear end in sight.

Inside Russia and in occupied areas of Ukraine, the Ukrainians have stepped up their attacks, particularly on energy infrastructure.

At least four people were killed and seven injured on Monday in shelling blamed on Ukraine in the occupied Lugansk region (east) and in the Russian region of Kursk, Russian authorities said.

Ukraine also claimed to have attacked an oil terminal and an electricity substation in the Belgorod and Lipetsk regions respectively, in western Russia, not far from the Ukrainian border.

The Russian side gave no indication of the attack on the oil terminal, but the governor of Lipetsk confirmed a fire at the electrical substation, without revealing its cause or accusing Ukraine.

JH // SCA

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