Russia has made its biggest advances in 18 months
Russia has made its biggest advances in 18 months AFP

Russian forces were pressing ahead Friday with their offensive in north-east Ukraine as Russian President Vladimir Putin said there were no current plans to occupy Kharkiv city, the regional capital.

On a trip to China, Putin said the latest assault was direct retaliation for Ukrainian shelling of Russia's border regions and that Moscow was trying to create a "security zone".

"This is their fault because they have shelled and continue to shell residential neighbourhoods in border areas," Putin told reporters, adding there was no intention at this stage to take Kharkiv, Ukraine's second city about 30 kilometres (18 miles) from the border where more than a million people still live.

Moscow launched the surprise offensive into Ukraine's north east on May 10, sending thousands of troops across the border and unleashing artillery fire on several settlements.

Both countries said Friday that Russian troops were continuing to advance, as Ukraine warned more heavy fighting lay ahead.

In a daily briefing, Russia's defence ministry said its army had "liberated 12 settlements in the Kharkiv region over the last week... and continues to advance deep into enemy defences."

Russian forces took control of 278 square kilometres (107 square miles) -- their biggest gains in a year-and-a-half -- between May 9 and 15, AFP has calculated using data from the Institute for the Study of War (ISW).

Most of that has been in the northeastern region, though its troops have also advanced in the south.

The Ukrainian governor of the Kharkiv region, Oleg Synegubov, said Russian forces were trying to surround Vovchansk, an almost deserted town which had a pre-war population of around 18,000.

"The enemy has actually started to destroy the town. It is not just dangerous to be there, but impossible," Synegubov said in a briefing.

He said Ukrainian troops were resisting the onslaught there, but warned Russia was gaining ground near Lukyantsi, a village around 20 kilometres (12 miles) northeast of Kharkiv city.

Kyiv pulled its troops back from that area earlier this week amid heavy fire and has rushed in reinforcements.

Ukraine army chief Oleksandr Syrsky said Russia was trying to force Ukraine to pull up even more troops from its reserves.

"We realise that there will be heavy fighting ahead and the enemy is preparing for it," he said.

Russia has a manpower and ammunition advantage across the front lines, and military analysts say the fresh offensive could be designed to further stretch Ukrainian troops and resources.

Ukraine has evacuated almost 9,000 people from the area in the week since Russia launched the offensive.

The city of Kharkiv has been targeted with intense Russian aerial bombardments, including for weeks ahead of the ground assault.

A rocket strike on the city on Friday afternoon killed one civilian and injured at least four others, Synegubov said in a post on Telegram.

Putin's comments about the need to protect Russian border zones came hours after Ukraine launched a wave of drones at Russia and the annexed Crimea peninsula overnight, killing two people including a child and setting oil infrastructure ablaze.

The attack was Ukraine's largest aerial offensive in weeks and one of many to target Russian energy facilities, which Kyiv says Moscow uses to fuel the war.

The Russian military said it had intercepted or downed more than 100 Ukrainian drones over the south of the country, Crimea and the Black Sea overnight.

Officials in multiple Russian regions reported damage.

One drone struck a family driving near the border in the Belgorod region, killing a mother and her four-year-old son, the region's governor Vyacheslav Gladkov said.

"The child was in a critical condition. Doctors did everything possible to save him. (But) to much grief, the four-year-old died in hospital," he said.

In the coastal town of Tuapse in the southern Krasnodar region, Ukrainian drones hit an oil refinery for the second time this year, sparking a large fire that was later put out, authorities said.

And several fires also erupted after a drone attack on Novorossiysk, a key port city also in the Krasnodar region, local governor Veniamin Kondratyev said.

A source in Ukraine's defence sector confirmed Kyiv had targeted oil facilities in both cities, and had also hit an electrical substation in the Russian-controlled port of Sevastopol on the annexed Crimean peninsula.

The city's Russian-installed governor Mikhail Razvozhayev said there had been a "partial blackout" after debris from downed drones damaged a substation, and that work to restore power was ongoing.

Moscow launched the surprise assault into Ukraine's Kharkiv region last week
Moscow launched the surprise assault into Ukraine's Kharkiv region last week AFP
Moscow launched the surprise assault into Ukraine's Kharkiv region last week
Moscow launched the surprise assault into Ukraine's Kharkiv region last week AFP