(Bloomberg) -- Ukrainian President Volodymyr Zelenskiy said his country is racing to complete 2,000 kilometers (1,200 miles) of defensive fortifications as Kyiv runs low on ammunition and Russian forces take to the offensive.  

The Ukrainian leader said he’s counting on the “timely completion” of the three-tiered defense system, according to a comment on Telegram after he received a report from Prime Minister Denys Shmyhal on Monday.

“The task is massive, but the tempo so far is good,” Zelenskiy said.

The construction effort reflects the shift in momentum in the two-year war, with Russian forces making gains as Kyiv’s military struggles with dwindling ammunition stocks. Ukraine failed to make progress last year in a counteroffensive backed by Western-delivered weaponry. 

The UK’s Defense Ministry said Sunday that Kyiv is “almost certainly” bolstering its defenses with anti-tank barriers known as dragon’s teeth, ditches, trenches and minefields. 

“It is highly likely the expansion of defensive lines will reduce Russia’s ability to advance or exploit tactical gains as part of its ongoing offensive operations,” the ministry said in a defense intelligence update on social platform X. 

Ukraine’s ambition to seize back territory from Russia has given way to concerns in Kyiv that the Kremlin could gain significant momentum by the summer unless NATO allies and others step up supplies. 

Zelenskiy’s top general, Oleksandr Syrskyi, said last month that Russia’s capture of the eastern city of Avdiivka was compounded by what he called mistakes by frontline commanders, which resulted in the retreat in the area. The fall of the city and several nearby villages fueled fears that Kyiv’s defenses may not be able to hold. 

A delayed start of Ukraine’s much-anticipated counteroffensive last summer gave Russia’s military months to prepare defenses along a 1,200-kilometer front line stretching from the Donbas region in eastern Ukraine to the mouth of the Dnipro River to the south. Those dug-in forces halted a Ukrainian advance. 

Russia by contrast is already turning up the pressure on Ukrainian troops, with Kremlin forces threatening positions across the frontline, including positions west of Avdiivka and Kupyansk in the northeastern Kharkiv region. 

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