Ukrainian officials said only a few hundred residents remained in the north-east town of Vovchansk outside Kharkiv amid pitched battles. Russia was attacking new areas with small groups to try to widen the front and stretch Ukrainian forces, said the Kharkiv regional governor, Oleh Syniehubov. “The situation is difficult.”

Russia’s forces were driving towards Vovchansk about 5km (3 miles) from the Russian border, as well as Lyptsi north of Kharkiv, Syniehubov said. Ukraine’s troops were trying to establish themselves at a meat plant on the outskirts of Vovchansk. About 5,700 people were evacuated from in and around Vovchansk and roughly 300 remaining were being urged to leave.

The Ukrainian army acknowledged Russia was “achieving tactical success” after launching its Kharkiv ground assault on Friday. The DeepState Telegram channel – which is close to the Ukrainian army – said Russia had taken about 100 sq km (39 square miles) of territory. Ukraine was mounting “constant fire”, including from drones, “but unfortunately it does not stop them”, the channel said.

Ukraine’s security council chief, Oleksandr Lytvynenko, said Moscow had mounted tens of thousands of troops against the Kharkiv region. “There are a lot of Russians, quite a lot. About 50,000 were on the border. Now there are much more than 30,000 coming.” On Monday evening, a missile hit Korotych, a settlement near the city of Kharkiv, killing a 38-year-old man and injuring three, police said. Earlier attacks injured a 71-year-old woman in Lyptsi and a man, 69, in the town of Izium, the governor said.

Ukraine launched drone strikes on western Russia, a security source in Kyiv told AFP, hitting an oil terminal in the Belgorod border region and an electrical substation in the Lipetsk region. Rockets struck the Luhansk region of eastern Ukraine under Russia’s control, according to Moscow-appointed governor Leonid Pasechnik. The attack on an industrial zone of the town of Sorokyne, known as Krasnodon in Russian, killed three and injured four, he said.

In the southern Kherson region, two people were found dead after a strike hit a residential building, regional military administration chief Oleksandr Prokudin said.

Ukraine’s security service, the SBU, said it thwarted a Russian operation in Kyiv to set off bombs disguised in packages of tea in builders’ markets, and a car bomb outside a cafe. A defence enterprise in the western city of Lviv was also a target. Two Russian military agents were detained on suspicion of involvement and 19 explosive devices were seized, the Ukrainian prosecutor general’s office said. The SBU said the four Kyiv bombs had been intended for detonation in the capital on 9 May when Russia celebrates victory over Nazi Germany in 1945. The Lviv attack was meant to happen in February, the SBU said.

In Spain, a pensioner who allegedly sent letter bombs to the Spanish PM and the US and Ukrainian embassies in 2022 went on trial Monday, facing 22 years behind bars if convicted. Pompeyo Gonzalez Pascual, a man in his mid-70s from northern Spain, was opposed to Spanish and US support for Ukraine after the Russian invasion and “sought to change those positions and cause a profound upheaval in Spanish society”, the court indictment said.

The US state department called it a sign of “desperation” after the Russian president, Vladimir Putin, removed his veteran defence minister Sergei Shoigu and replaced him with a top economic official, Andrei Belousov.

Britain’s opposition Labour party affirmed its “ironclad” commitment to Ukraine during a visit to Kyiv on Monday by the party’s foreign and defence shadow ministers David Lammy and John Healey. Britain’s Labour party polls well ahead of the governing Conservatives with a national election expected later this year.