Ukrainian President Volodymyr Zelensky said in an exclusive interview with AFP on Friday he expects Russia to step up its offensive in the northeast and warned Kyiv only has a quarter of the air defences it needs to hold the front line.
Russian forces, which made only moderate advances in recent months, launched a surprise assault in Kharkiv region on May 10 that has resulted in their biggest territorial gains in a year-and-a-half.
Zelensky said Russian troops managed to advance between five to 10 kilometres (3-6 miles) along the northeastern border before being stopped by Ukrainian forces, but added that the region could be the "first wave" in a wider offensive.
"I won't say it's a great success (for Russia) but we have to be sober and understand that they are going deeper into our territory," he said, speaking from Kyiv in his first interview with foreign media since the offensive began.
Zelensky said the situation in Kharkiv region has been "controlled" but "not stabilised".
He doubled down on pleas to allies to send more air defence and fighter jets to combat Russia's air superiority as the war grinds through its third year.
"Today, we have about 25 percent of what we need to defend Ukraine. I'm talking about air defence," he said.
Ukraine needs "120 to 130" F-16 fighter jets or other advanced aircraft to achieve air "parity" with Russia, Zelensky said.
- Kharkiv offensive -
Russian President Vladimir Putin said during a trip to China this week the northeastern offensive was in retaliation for Ukraine's shelling of border regions and that Moscow was trying to create a "security zone".
Russian forces have taken 278 square kilometres (107 square miles) between May 9 and 15, their biggest gains since the end of 2022, AFP calculated using data from the Institute for the Study of War (ISW).
Both countries said Russian troops are still advancing, while Moscow's defence ministry said its forces have captured 12 villages in the Kharkiv region so far.
Ukraine has evacuated almost 9,000 people from the northeast border area since Russia launched the assault.
Putin said there was no intention at this stage to take Kharkiv, Ukraine's second city, about 30 kilometres (18 miles) from the border. More than one million people still live there.
The Ukrainian governor of the Kharkiv region, Oleg Synegubov, warned however that 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 this week amid heavy fire and has rushed in reinforcements.
Military analysts say the northeastern offensive could aim to further stretch Ukrainian troops and resources, with Russia pressing its manpower and ammunition advantage.
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.
- Mobilisation law -
As he anticipates a widening Russian offensive, Zelensky acknowledged issues with staffing and "morale" within Ukraine's often outgunned and outmanned ranks.
"We need to staff the reserves... A large number of (brigades) are empty," Zelensky told AFP.
With no end to the war in sight, Ukraine's army is struggling to recruit, while fighters are growing exhausted and angry at the lack of rotation.
Many Ukrainian soldiers have been fighting for more than two years without the possibility of being discharged.
Under a controversial mobilisation law that comes into force Saturday, Kyiv has lowered the age at which men can be drafted from 27 to 25 and tightened punishments for those who avoid being called up.
But lawmakers scrapped a proposal to grant soldiers who have served for more than 36 months the option to be discharged.
On Friday, Zelensky also signed a law allowing prisoners to be recruited in exchange for parole.
As Western allies press for a quick end to the war, Zelensky insisted Ukraine is still playing the long game.
"The West wants the war to end. Period. As soon as possible. And, for them, this is a fair peace," he said.
But for Ukraine, "final victory will lead to Russia's defeat".
- 'Human shields' -
Ukrainian authorities said Russian forces have begun destroying Vovchansk, an almost deserted town near the border which had a pre-war population of around 18,000.
They have also accused them of capturing dozens of civilians to use as "human shields" to defend their command headquarters.
AFP was not able to immediately verify the claim.
Kyiv launched one of its largest aerial attacks in weeks overnight Thursday to Friday, launching drones at Russia and the annexed Crimea peninsula.
The Russian military said it intercepted or downed more than 100 Ukrainian drones over the south of the country, Crimea and the Black Sea.
Officials in multiple Russian regions reported damage.
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 extinguished, authorities said.
Several fires also erupted after a drone attack on Novorossiysk, a key port city also in the Krasnodar region, local governor Veniamin Kondratyev said.