PRAGUE (Reuters) - The slow pace of donor contributions poses the main obstacle to shipping desperately needed ammunition to Ukraine faster, a leading official in the Czech drive to supply Kyiv said on Thursday.

Speaking on the sidelines of a NATO meeting in Prague, Tomas Kopecny said Ukraine would need large-calibre ammunition worth 7 billion euros to 10 billion euros ($7.6 billion to $10.8 billion) annually, equal to about 200,000 rounds per month.

That would get it on par with Russia, which is also sourcing supplies in some of the same markets, Kopecny said.

The Czech government's envoy for Ukraine and one of the key figures behind the Czech-led initiative to raise contributions from allies to supply Ukraine said there was a single-digit million number of shells available on the global market over a one-year horizon.

"The pace of deliveries depends on a single thing," Kopecny said. "Availability of financial resources."

Kopecny said the Czechs so far had payments or firm commitments for around 1.7 billion euros from 15 donor countries, which was enough for half a million rounds to be delivered by the end of the year.

About 20 countries have pledged to take part in the Czech initiative, but only five have so far delivered payments, he said - Germany, the Netherlands, Denmark, Portugal and Canada, with Germany leading the pack.

"We have the five who are dedicated enough and fast enough, then we have 10 who are dedicated enough, have clear commitment ... and then we have a few who have not shown much of an action," he said.

Kopecny said the Czechs had arranged shipping of 1.3 million artillery rounds to Ukraine from the start of the war until the February 2024 announcement of the current initiative, showing the pledges made since were somewhat underwhelming.

The ammunition is sought on a global market often open to all sides, he said. Speed is therefore essential to make prepayments - with other traders or even Russia competing for them.

Kopecny reiterated Ukraine would get the first shipment under the umbrella of the Czech initiative in June, and said the amount would be between 50,000 and 100,000 rounds.

The Czech initiative is not the only effort to arm Ukraine. The United States and other countries send ammunition through other channels, and Ukraine is also producing and procuring ammunition on its own.

Kopecny said the amounts needed paled in comparison with how much governments had spent on measures amid the coronavirus pandemic or the cost of the war in Afghanistan.

"It's so frustrating when you compare it with the expenses and with the loans used for COVID. Hundreds of billions of euros there - and here we're struggling with hundreds of millions," he said.

($1 = 0.9224 euros)

(Reporting by Jan Lopatka and Sabine Siebold; Writing by Jan Lopatka; Editing by Alison Williams)

By Jan Lopatka and Sabine Siebold