PRAGUE - It will take 10-15 years to refill Western stocks of artillery ammunition depleted to support Ukraine's army as it battles Russia's invasion, according to the owner of major arms manufacturer Czechoslovak Group.

Despite the flow of ammo to Ukraine, CSG owner Michal Strnad said Ukrainian forces were experiencing shortfalls as Western governments were running down their arsenals amid limits on production capacity.

Strnad told Reuters his firm was now responsible for about 25-30% of European output of NATO-standard 155mm artillery.

"Artillery ammunition are very scarce goods today," he said in an interview. "I estimate it will take 10-15 years to refill (Western armies') stocks" as a result of the war in Ukraine.

Strnad said CSG now had capacity of 80,000-100,000 of artillery shells per year, a significant chunk of the annual capacity in Europe which he put at 270,000-300,000.

The firm is hiring 250-300 more people to expand production, he said, aiming to raise capacity to 150,000, but this would take about two years to set up due to lengthy delivery times of production equipment.

European governments have significantly drawn on their arsenals to support Ukraine, which Strnad said was firing 40,000 shells per week from several hundred, Western-supplied howitzers against Russian invaders.

"Really a lot has been delivered to Ukraine," he said. "But the fact is that today the Ukrainians are shooting less than they could because they do not have enough ammunition."

CSG has been a major supplier of upgraded Soviet-era weapons to Ukraine, including tanks, artillery pieces, multiple rocket launchers and infantry fighting vehicles.

Its supplies include 90 modernised T-72 tanks, paid for by the United States and Netherlands, a process now underway.

But CSG's stocks of Soviet-era weaponry have also dwindled and there is little left on the market that could be quickly modernised and send on to Ukraine, Strnad said.

(Reporting by Jan Lopatka)