Ukrainian troops have withdrawn from the key battleground town of Avdiivka in the east of the country which could pave the way for a Russian advance as the war nears its second anniversary. 

The withdrawal, announced as Ukraine faces acute shortages of ammunition with U.S. military aid delayed for months in Congress, aimed to save troops from being fully surrounded by Russian forces after months of fierce fighting, Kyiv said.

Most of the city’s pre-war population of 32,000 people has already left, and the town has been almost completely destroyed.

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General Oleksandr Syrskyi, who took the helm of the Ukrainian military in a major shakeup last week, announced the withdrawal as a tactical move to save the lives of troops in a town that has been under heavy attack for months.

"I decided to withdraw our units from the town and move to defense from more favorable lines in order to avoid encirclement and preserve the lives and health of servicemen."

"Our soldiers performed their military duty with dignity, did everything possible to destroy the best Russian military units, inflicted significant losses on the enemy in terms of manpower and equipment," he said.

Russia stepped up its offensive on Avdiivka in October and Ukraine's position had been looking increasingly fraught for weeks.

The Third Assault Brigade, a prominent Ukrainian infantry assault unit, was rushed into the town to help reinforce troops this week as other Ukrainian forces pulled back from the southeast of the town. The unit described the fighting as "hell" and said on social media that Ukrainian defenders had been outnumbered by Russian forces by a ratio of about six to 100 in some places.

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The withdrawal is seen as a massive win for Russian President Vladimir Putin, and the biggest since Russia captured the city of Bakhmut in May 2023.

The timing is critical as Russia is looking for a morale boost ahead of the second anniversary on Feb. 24 of Moscow’s full-scale invasion of Ukraine and the March presidential election in Russia. It also comes in the wake of news that Putin critic and opposition leader Alexei Navalny has died at the age of 47.

It comes just days after National Security Council spokesperson John Kirby said the town was at risk of falling into Russian control.

"This is happening because Ukrainian forces on the ground are running out of artillery ammunition," Kirby said during a press briefing Thursday. 

"Russia is sending wave after wave of conscript forces to attack Ukrainian positions, and because Congress is yet to pass the supplemental bill, we've not been able to provide Ukraine with the artillery shells that they desperately need to disrupt these Russian assaults."

The United States is Ukraine’s biggest single supporter but some $60 billion for Kyiv is being held up by political disagreements among American lawmakers.

Earlier this month, all 27 countries of the European Union agreed on a €50 billion ($54 billion) financial aid package to Ukraine.

The withdrawal came a day after Ukrainian President Volodymyr Zelenskyy on Friday made another trip to western Europe, hoping to press his country’s Western allies to keep providing military support.

Speaking at the Munich security conference on Saturday, Zelenskyy urged Western countries to help Ukraine defeat Putin, saying that the war poses a threat to the entire world.

"How long will the world let Russia be like this? This is the main question today," Zelenskyy said.

"Please, everyone in the world, do not ask Ukraine when the war will end. Ask yourself – why is Putin still able to continue it. Let’s not fear Putin’s defeat and the destruction of his regime. Let’s instead – work together to destroy what he stands for. It is his fate to lose, not the fate of the rules-based world order to vanish. And may our world, based on rules, never become the world of yesterday."

The Associated Press and Reuters contributed to this report.