Smoke rises after a military strike on a compound of Sievierodonetsk's Azot Chemical Plant, amid Russia's attack on Ukraine, in the town of Lysychansk, Luhansk region, Ukraine June 10, 2022. Picture taken June 10, 2022.
Smoke rises after a military strike on a compound of Sievierodonetsk's Azot Chemical Plant, amid Russia's attack on Ukraine, in the town of Lysychansk, Luhansk region, Ukraine June 10, 2022. Picture taken June 10, 2022. Reuters / STRINGER

Ukraine will defend its eastern front from higher ground in the city of Lysychansk after withdrawing from a Russian onslaught in its sister city and Kyiv will try to stabilise the situation, Ukraine's military spy chief said on Saturday.

Russia has been replenishing forces with reservists as part of a covert mobilisation and it is pointless to hope Moscow will simply run out of troops in this war, Kyrylo Budanov told Reuters.

The 36-year-old head of the Defence Ministry's shadowy Main Directorate of Intelligence spoke in a rare interview in Kyiv hours before Russia claimed full control of the city of Sievierodonetsk where Ukrainian forces had been bombarded for weeks.

Russia used the tactic "it used in Mariupol: wiping the city from the face of the earth. Given the conditions, holding the defence in the ruins and open fields is no longer possible. So the Ukrainian forces are leaving for higher ground to continue the defence operations," he said.

The only way path to victory for Ukraine, he said, was through sheer military force in order to retake all its territory.

"The strategy is very simple. Stabilise the situation. Receive the required amount of equipment and prepare the required amount of forces and means to start the counter-offensive to return all our territory," he said.

The interview took place in a heavily guarded office. An automatic weapon lay on his desk along with an array of folders. Sandbags were piled up in the windows.

Budanov estimated that 330,000 personnel were involved in Russia's operations in Ukraine, a third of its entire armed forces, a figure he added also included non-combat personnel such as logistics staff.

"The main part of this number is the combat element and that is more than 50% of what Russia has at the moment," he said.

He said he was calm about the possibility of Russia eventually openly announcing a mobilisation as it would mean Kremlin leader Vladimir Putin facing awkward questions at home.

"They really fear this - this is the main reason why the mobilisation is happening in a hidden way, particular by using," reservists, he said.

"The military units that took part on Feb. 24 and those same military units now are in most cases on their second and in some cases even their third group of personnel," he said.

Moscow has so far stopped short of calling a general military mobilisation in what it calls a special military operation in Ukraine.

Budanov declined to comment in any detail on Ukrainian partisan resistance efforts in occupied parts of Ukraine, but used menacing language for partisan targets.

"Those people who betrayed Ukraine and all those wretches who came here to destroy our country will be destroyed. There is no other objective," he said.

He declined to elaborate on any plans for a counteroffensive in the occupied region of Kherson that Russia seized at the beginning of its Feb. 24 invasion.

"From August we should expect visible results of military activity from Ukraine. Just wait a bit and we'll see what it brings," he said.

He said any counteroffensive would hinge on various factors including having a well-equipped concentration of forces, which would depend on Ukraine getting help from foreign partners.

He voiced huge gratitude to the West for support, but said that Ukraine needed more help four months into the war, including weapons systems for carrying out strikes and armoured vehicles.