Ukraine has been promised more than a million artillery shells under a Czech initiative to buy them on the world market.
Nato allies including Germany and Canada have pledged money to the Czech plan after a failed push to produce enough ammunition in Europe.
A stockpile of 800,000 shells offered by Czech President Petr Pavel could rise to 1.5 million after more potential supplies were identified.
Ukrainian troops “need ammunition right now” and its allies “cannot wait until European companies are ready”, said Mr Pavel, a former army general.
“That’s why we are trying to acquire the ammunition wherever it is, to deliver it to Ukraine as fast as possible, in parallel increasing our own capacity.”
Ukraine says it needs more artillery to counter Russia's bigger arsenal and fight off attacks in the war's third year.
The shells in the Czech shopping basket include 155mm artillery used by Nato forces and Soviet-era 122mm ammunition.
Germany will meet the cost of about 180,000 munitions, with delivery set to begin in the summer, Defence Minister Boris Pistorius said.
He said Germany would also provide 10,000 munitions directly from its own armed forces as part of a new €500 million ($542.5 million) aid package.
Finland is contributing the equivalent of $32.6 million and Canada $29.4 million. Canada will also provide night-vision equipment and more than 800 drones, said Defence Minister Bill Blair.
“Ukrainian officials have been clear that they need more artillery ammunition, rapidly,” he said.
Ukraine welcomed the ammunition push even as it continues to ask for more equipment, including air defences and F-16 fighter jets.
Pressure is building on Europe to take more of the burden, as US aid is held up in Congress and the prospect of a second Donald Trump presidency hangs in the air.
European allies plan to buy more equipment to send a message to Russia that western support will “not let up”, said German Chancellor Olaf Scholz at a summit on Ukraine last week.
The EU had pledged to provide a million rounds of artillery. However, it concedes that it will not hit the target within a year as it had hoped.
Billions of dollars are being poured into defence procurement as Europe tries to become more self-reliant and reinforce its defences against Russia.
EU countries will consider using frozen Russian assets to pay for military aid. It is also hoped that Ukraine could produce more arms in its own factories.
“In the near future, European companies will be able to provide a sufficient amount of ammunition,” Mr Pavel said.
