KHARKIV, Ukraine, May 17, 2024 (BSS/AFP) - Ukraine battled Thursday to "stabilise" the front line in the northeast Kharkiv region, where Moscow has made its largest territorial gains in 18 months after launching an offensive last week.

President Volodymyr Zelensky said more reinforcements had been sent to the area, and the Ukrainian army said it had partially halted Russia's advance.

But the head of the Kharkiv region said Moscow had gained ground near the border village of Lyptsi and had "not given up" capturing the town of Vovchansk.

"Our task at the moment is to stabilise the front line," said Governor Oleg Synegubov.

Ukraine accused Russian troops of executing civilians in territory it had captured, and of using some civilians in Vovchansk as "human shields".

Late Thursday, the Ukrainian army said there had been "no significant changes" on the front lines, including in Vovchansk, even if some troops had to "regroup" in the Pokrovsk area near Donetsk due to "intense fire and assault actions".

Russian latest offensive has further stretched Ukraine's outgunned and outmanned forces.

Moscow seized 278 square kilometres (107 square miles) of Ukrainian territory between May 9 and 15, according to AFP calculations based on data from the Institute for the Study of War (ISW) -- the largest territorial gain in a single operation since mid-December 2022.

- 'Extremely difficult' -

Zelensky met military leaders in Kharkiv city, around 30 kilometres (18 miles) 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 social media post.

"However, the area remains extremely difficult. We are reinforcing our units.

"Our defence forces have partially stabilised the situation," army spokesman Nazar Voloshin said on state TV.

Russia's ability to make further breakthroughs may be limited by a lack of forces, a top NATO commander said.

"The Russians don't have the numbers necessary to do a strategic breakthrough... more to the point, they don't have the skill and the ability to do it," US General Christopher Cavoli, NATO Supreme Allied Commander Europe, told journalists in Brussels.

"I've been in very close contact with our Ukrainian colleagues and I'm confident they will hold the line," Cavoli said after Ukraine's military briefed NATO's top brass.

- 'Killed by Russians' -

Ukraine accused Russia of capturing and killing civilians in the border town of Vovchansk and of keeping about 35 to 40 people as "human shields".

"According to operational information, the Russian military, trying to gain a foothold in the city, did not allow local residents to evacuate," Interior Minister Igor Klymenko said.

"They began abducting people and driving them to basements," he added.

"The Russians keep them in one place and actually use them as a human shield, as their command headquarters is nearby," said Sergiy Bolvinov, head of the Kharkiv region's police investigation department.

AFP could not verify the claims, and there was no immediate response from Moscow to the allegations.

Ukraine has evacuated about 8,800 people since Russia launched the new assault, Synegubov said. Some arrived at a humanitarian centre in Kharkiv on Thursday.

Among them was 85-year-old Nadezhda Borodina, who had her dog Vasik on a leash and her frightened cat Lucas packed in a plastic bag.

Ukrainian "soldiers arrived and shouted 'Let's go, let's go!' and we were gone in five minutes," she said.

Meanwhile, Ukrainian shelling killed four women in the Russian-held city of Donetsk in eastern Ukraine, local Russian-installed authorities said.

And a Ukrainian drone strike on border villages in Russia's Belgorod region killed a mother and her four-year-old child, the regional governor said early Friday.

- 'All fronts' -

Most of Russia's recent gains are in the Kharkiv area, though they have also claimed fresh territory in the eastern Donetsk and southern Zaporizhzhia regions.

Following months of stalemate on the front lines, Russia has seized the battlefield initiative, pushing on from the capture of industrial hub Avdiivka in February.

Russia's defence ministry said the army had "advanced deep into the enemy's defences" in the Kharkiv region.

Some military analysts say Moscow may be trying to force Ukraine to divert troops from other hot spots, such as around the strategic hilltop town of Chasiv Yar in the Donetsk region.

Russia said Wednesday its forces had captured the village of Robotyne in the Zaporizhzhia region, around 300 kilometres (185 miles) south of Moscow's new offensive.

The settlement was one of the few Ukraine successes in a disappointing counter-offensive last summer.

The intensification of Russian attacks has underscored the acute ammunition and manpower shortages crippling the Ukrainian military.

In China for a state visit, Putin said he was "grateful" to Beijing for "the initiatives they are putting forward to resolve" the war.

There are no indications Moscow and Kyiv are prepared to engage in direct talks, which Ukraine says would only be used by Russia to buy time to prepare for a new assault.