Kyiv, Ukraine – Because of the incessant, crackling cannonade around him, the police officer had to yell.

“The enemy is taking positions on the streets of Vovchansk, so people, do get evacuated,” the bearded officer in a flak jacket and helmet urged residents of the Ukrainian town, which is near Russia’s border.

His call was filmed and posted to Telegram on Wednesday. As Russia’s war on Ukraine escalates, it has been viewed more than 13,000 times since.

Vovchansk is an industrial town in the northeastern Kharkiv region that sits just 5km (3 miles) away from the Russian border and has been under attack since Friday.

That’s when Russian forces began their two-pronged raid on the region and seized almost a dozen villages within days.

With its apartment and factory buildings that can be defended by small groups of servicemen, Vovchansk is a harder nut to crack.

The Russians are still trying to seize an unused airfield and Soviet-era slaughterhouse that could serve as a base for further advancement.

The second direction of their offensive began in the border town of Liptsy, about 50km (31 miles) west of Vovchansk.

It sits on a highway leading to the regional capital, also called Kharkiv.

Ukraine’s second-largest city with a pre-war population of 1.5 million, Kharkiv has been bombarded almost non-stop in recent months.

So far, the raid is Russia’s largest ground attack on Ukraine since August 2022, when the Ukrainian military kicked out the invaders from most of the Kharkiv region.

“This is a successful combat reconnaissance, they advanced on a tactical level,” Lieutenant General Ihor Romanenko, a former deputy chief of Ukraine’s general staff of armed forces, told Al Jazeera.

Russian President Vladimir Putin said Moscow wants to create a “sanitary zone” in Kharkiv to protect the Russian region of Belgorod that lies north of it and has been heavily shelled by Ukrainian forces.

And even though Ukrainian intelligence reported weeks ago that the Russians would attack the region, Ukrainian forces failed to create a stable defence line to prevent the invasion, Romanenko said.

“The situation there is difficult,” he said.

But so far, the Russians don’t seem to have enough forces – at least 150,000 servicemen are needed to siege the city of Kharkiv as their current contingent along the border is about three times smaller, Romanenko said.

Moscow, however, is conducting a “hidden mobilisation” of hundreds of thousands of men and may deploy larger forces to seize Kharkiv by late May or early June, he said.

“We can gather resources, form a defence system and thwart their plan of an offence,” he said.

Moscow’s push in Kharkiv may seem concerning, but “given the challenges Russia faces they are unlikely to lead to operationally important penetration and exploitation”, retired NATO general Gordon “Skip” Davis Jr told Al Jazeera.

Russia has employed a significant number of combat vehicles in the Kharkiv direction supported by intense air support with the apparent attempt to fix Ukrainian forces in the north to allow advances to the south, he said.

“These advances would allow Russian forces to gain territory of the illegally annexed regions that remain under Ukrainian control,” he said.

Russia’s aerial superiority

One of the factors of their success is aerial superiority undisputed since the war began in 2022.

The ground assault is backed by Russian bombers that throw heavy glide bombs capable of destroying even the most fortified buildings.

These bombs played a crucial role in Moscow’s recent gains in the eastern Donetsk region.

Ukraine got rid of most of its Soviet-era air force, transferring all of its strategic bombers to Russia in the late 1990s as payment for natural gas debts.

Western powers agreed to supply several dozen F-16 fighter jets, but the first six are only expected in summer.

Another great hindrance is a taboo on the use of NATO-supplied weaponry on Russian territory as Western leaders are afraid of antagonising Putin.

Therefore, Moscow’s troops “are exploiting adjacent Russian land and airspace that have essentially become sanctuary from Western-provided long-range fire systems and munitions”, Davis said.

“It is time for Western leaders to remove these externally imposed restrictions and allow Ukraine to defend itself effectively with all the means available.”

The US Helsinki Commission, a human rights group, said on Wednesday that the White House “must not only allow but encourage the Ukrainian armed forces to strike Russian forces firing and staging in Russian borders and share intelligence to prevent massive loss of life”.

The White House seems to be wavering.

“We have not encouraged or enabled strikes outside of Ukraine, but ultimately Ukraine has to make decisions for itself about how it’s going to conduct this war,” US Secretary of State Antony Blinken said earlier on Wednesday.

Meanwhile, Russian servicemen pay a heavy price for their success.

Those who refused to take part in front-line assaults on Ukrainian trenches – that typically leave next to no survivors – were killed by other Russian servicemen, according to Kyrylo Sazonov, a Ukrainian military analyst.

Sazonov posted on his Telegram channel written refusals that were found on the bodies of four Russian servicemen killed near the village of Staritsa.

Ukrainian counterattacks forced Russians to leave the village of Zelene which sits on the way to the city of Kharkiv.

“On this segment of ‘Russia’s big advance towards Kharkiv’ its speed fell almost to zero,” military analyst Konstantin Mashovets wrote on Telegram on Thursday.

Western analysts agree with him.

The speed of Moscow’s offensive in Kharkiv “continues to decrease after Russian forces initially seized areas that Ukrainian officials have now confirmed were less defended”, the Institute for the Study of War, a think tank, said on Thursday.

Many Kharkiv residents, however, feel disoriented and scared.

“This feels like a recurring nightmare,” said Oleksandra Bondarenko, a 42-year-old sales assistant who fled Kharkiv in 2022 to settle in Kyiv with her teenage daughter and two cats.

“Europe and America are bickering about whether they should give us planes or missiles, voting on military aid, and the Russians are simply not stopping,” she told Al Jazeera outside the grocery shop in central Kyiv where she works, nervously puffing on a cigarette.

“Democracy doesn’t seem to be working during a war, and for us, this means endless losses.”