Russia’s offensive in Ukraine’s northeastern border region of Kharkiv may just be the “first wave” in a wider assault, Ukrainian President Volodymyr Zelenskyy has warned as he appealed to allies to send more air defence and fighter jets.

Russian forces, which had made only moderate advances in recent months, launched a surprise assault in the Kharkiv region on May 10 that resulted in their biggest territorial gains in a year and a half.

Zelenskyy conceded on Friday, in an interview with the AFP news agency, that Ukraine only has a quarter of the air defences it needs to hold the front line while the war grinds on.

He said Russian forces managed to advance between five to 10km (3-6 miles) along the northeastern border before being stopped by Ukrainian forces.

On Saturday, Kharkiv’s Governor Oleg Synegubov said “a total of 9,907 people have been evacuated” from the region following a ground attack by Russian troops.

Present Ukraine is “outmanned in terms of soldiers” in parts of the front line even before the latest Russian attacks.

“Ukraine said that there were seven Russian soldiers to one Ukrainian soldier, so that’s going to put fresh pressure on them,” he said.

In an effort to increase troop numbers, Zelenskyy signed two laws, one to enable prisoners to join the army and another that increases fines for draft dodgers fivefold, which took effect on Saturday.

Ukraine’s mobilisation age remains high at 25, while Russia’s is 18, Holman reported, adding that the government was reluctant to “hollow out its already small number of younger men by calling them up”.

The new legislation is aimed at shoring up a depleted – and ageing – army.

“We need everyone. Older people because they’re more experienced in their specialty. But if we’re talking about some combat positions, where there should be endurance, physical condition and cold-bloodedness, those should be filled by young people,” Yaroslava Kashka, head of recruitment at the 12th Azov Brigade.

Zelenskyy also acknowledged that Russian forces were “going deeper into our territory”, adding that in order to achieve at least a level of air “parity” with Russia, Ukraine needs “120 to 130” F-16 fighter jets or other advanced aircraft.

“Today, we have about 25 percent of what we need to defend Ukraine. I’m talking about air defence,” he told AFP.

President Vladimir Putin said on Friday that the offensive in the Kharkiv region is aimed at creating a buffer zone and Russia has no plans to capture the city of Kharkiv.

Speaking to reporters while on a visit to China, Putin said Moscow launched its attacks in response to Ukrainian shelling of Russia’s neighbouring Belgorod region.