Russia is outgunning Ukrainian forces sixfold on the front lines, causing losses of troops and positions, Ukraine's recently appointed commander-in-chief Oleksandr Syrsky said in a rare interview published on Friday.

"A few days ago, the enemy's advantage in terms of ammunition fired was about six to one," Syrsky told the Ukrinform news agency.

"The defence forces are now performing tasks along the entire vast front line, with little or no weapons and ammunition," he warned, saying the situation was "tense" in some areas.

Syrsky took over as commander-in-chief in February after Ukrainian President Volodymyr Zelensky fired his popular predecessor, Valery Zaluzhny.

Syrsky added that in recent months and weeks, Russia had "significantly increased aviation activity, using KABs -- guided aerial bombs that destroy our positions".

Ukraine is pushing for the United States Congress to pass a long-stalled $60-billion military aid package for Kyiv.

"We hope to receive from our partners more air defence systems and, most importantly, missiles," Syrsky said.

"We would be even more grateful if this aid came faster and in sufficient quantities."

Ukraine has lost territory it would "undoubtedly have retained" with "a sufficient number of air defence systems and artillery shells", the commander-in-chief said.

"We have to admit that we were not able to achieve greater success during the Kharkiv offensive because we lacked resources," Syrsky said.

  'Our defence was compromised' 

 Ukraine recaptured territory near the eastern city of Kharkiv from Russia in 2022 but Russia continues to attack the border region.

Syrsky warned Russia against attempting to retake Kharkiv, Ukraine's second largest city, saying it would be "fatal for them".

"The lack of resources and the necessary amount of ammunition allowed the Russians to dig deep into the ground in the south of Ukraine, in Zaporizhzhia region," Syrsky added.

Russia built up lines of heavy defences in the south that Ukraine failed to break through in its summer counter-offensive last year.

"The assault on these positions, without effective air support, cost us human and equipment losses," Syrsky said.

"The latest case is Avdiivka," he added, referring to the frontline city near the eastern city of Donetsk, which Russia seized in February.

"Due to the constant bombardment with guided aerial bombs, the integrity of our defence was compromised," Syrsky said.

"The lack of ammunition for our artillery also played a negative role. This made it impossible to conduct an effective counter-battery fight," he added.

"To avoid encirclement and save lives, I decided to withdraw from Avdiivka."