Ukraine's new army head Oleksandr Syrsky, who was appointed in Kyiv's largest military shake up since Russia invaded, is taking the helm at a precarious moment in the war.
After nearly two years of fighting, these are the five most pressing challenges the 58-year-old commander, who was born in Russia, is facing.
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Foreign aid
Ukraine's allies, particularly Washington and Brussels, are struggling to keep up aid packages that have so far allowed Kyiv to hold out against Russia.
The EU this month unblocked 50 billion euros in aid, but US senators have only managed to clear a first hurdle to a potential future package after months of political deadlock.
The uncertainty over Ukraine's resources come as Russia turns it economy to a war footing, ramping up production and recruitment.
Mobilization
Ukraine's military and political leadership are at odds over how to replenish the army's ranks, following two years of costly fighting that Washington believes has killed around 70,000 Ukrainian soldiers.
Syrsky's predecessor had urged President Volodymyr Zelensky to add 500,000 servicemen to the army, but the Ukrainian leader rejected the unpopular appeal and advocated a more efficient rotations systems.
Mobilization legislation is working its way through parliament while exhausted and depleted Ukrainian units appealing for rotations off the front are meanwhile struggling to hold back waves of Russian forces.
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Defense lines
Ukraine's failed counteroffensive last summer crashed into nearly impenetrable Russian defensive lines, which Kyiv now wants to replicate across the front to frustrate slow by steady Russian advances.
Entrenching is a difficult task given the front line stretches some 1,000 kilometers (620 miles) and Ukrainian forces are facing oncoming assaults in eastern hotspots like Avdiivka and Kupiansk.
Ukraine's airspace
Zelensky has made it a priority for Ukraine this year to gain control of its airspace as it faces down waves of Russian drone and missile attacks.
Yet even after the West bolstered Ukraine's air defense systems, securing ammunition for those weapons remains an issue.
Syrsky also faces the dilemma of whether to utilize the systems for defense or in an offensive ways to target Moscow's airforce on Russian territory or over the Black Sea.
Ukraine, which is also expecting to take deliveries of F-16 fighter jets this year, says controlling the airspace over the country is key to making advances on the front.
Shoes to fill
The outgoing army chief, Valery Zaluzhny, was one of the most respected and trusted public figures in Ukraine with recent polling showing he had won the trust more than 90 percent of Ukrainians.
By contrast, surveys in December showed nearly 50 percent of the country had never heard of Syrsky.
In Ukrainian media, he has been presented as indifferent to military casualties, a reputation he appeared to confront in a statement describing soldiers' lives as the "main asset" of the army.
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