Ukrainian servicemen
A Ukrainian serviceman walks past a recruiting poster in Kyiv on April 23, 2024 AFP

The United States is the first to acknowledge that its long-awaited $61 billion aid package for Ukraine is not a "silver bullet."

As weapons and ammunition are rushed to the country, other issues such as manpower shortages in Kyiv's struggling military have come to the fore.

Meanwhile, the monthslong delay in passing the aid package -- caused by wrangling among US lawmakers -- has further weakened Ukraine's position on the battleground, according to analysts.

President Joe Biden, who quickly signed the law Wednesday after it passed Congress, said the bill "should have gotten there sooner."

Jake Sullivan, his National Security Advisor, said the aid package "will make a difference," but warned "there is no silver bullet in this conflict."

"One capability is not going to be the ultimate solution," Sullivan told a White House briefing, though he added "Ukraine's position in this conflict will improve and we believe that Ukraine can and will win."

Kyiv has been heavily reliant on billions of dollars of US military aid in its war with Russia following Moscow's full-scale invasion in February 2022.

But in recent months Ukrainian forces -- outgunned and outmanned -- have struggled to hold back Russian troops.

And in the United States -- Ukraine's largest provider of military assistance -- a bogged-down Congress had not approved large-scale funding for Kyiv since December 2022 before the new package was passed this week.

It contains nearly $14 billion to train, equip and finance the needs of the Ukrainian army.

Garret Martin, of the American University School of International Service in Washington, said the delay by US lawmakers in passing the aid package "had a cost."

"The aid can shore up Ukraine but it's not a magic wand that could fix all the challenges they face," Martin said.

"What the package cannot do is deal with the shortage of manpower," he added.

Biden and his Ukrainian counterpart Volodymyr Zelensky have discussed the manpower issue, according to the White House.

In April, Kyiv reduced the minimum age for military conscription from 27 to 25, making thousands more men eligible for the draft.

And this week, it stopped issuing new passports abroad to military-aged Ukrainian men, as part of measures to push them to return home and fight.

Max Bergmann, of the Center for Strategic and International Studies, said that the impact of American aid would depend on European efforts.

"European nations need to ramp up (weapons) production now," Bergmann said.

"Europe's goal should be to put itself in a position to potentially fill a future gap left by the United States should it not pass another supplemental."

Bergmann said that Ukraine should use 2024 to "hold the line, exhaust and attrit Russian forces," with next year possibly presenting an opportunity for a Kyiv offensive.