Ukraine faces its most difficult winter in modern history but should manage to reach a government goal of building 19 billion cubic meters (bcm) of natural gas reserves in time, Energy Minister German Galushchenko said on Thursday.

Ukraine abandoned Russian natural gas imports in 2015 and now gets its gas from the rest of Europe, but soaring prices and the huge cost of Russia's Feb. 24 invasion have called into question the feasibility of building up such a large amount of fuel. Russia calls its actions a "special military operation."

Reaching the prime minister's reserve target of 19 bcm could reassure Ukrainians bracing for a difficult wartime winter of serious energy shortages, as natural gas is largely used to heat homes.

"I think that during this season we will more or less reach 19 billion," Galushchenko told Reuters, noting the country needs part of these gas volume as insurance in "critical situations."

The government does not disclose its estimates of domestic gas consumption, but Galushchenko said he believed there was enough fuel to get through the winter.

But he predicted the looming winter would be Ukraine's worst since it gained independence from the Russia-dominated Soviet Union in 1991.

"There's no doubt about that - and not only for Ukraine but also for Europe. There will be challenges that Europe has never seen before," he said.

The minister declined to say what amount of gas had already been pumped into storage.

National energy company Naftogaz's head Yuriy Vitrenko told reporters earlier this month that more than 12 bcm of gas was already in storage.

It is unclear where Ukraine will source the remaining 7 bcm. Ukraine's central heating season typically begins in mid-October. Ukraine built up around 19 bcm of gas in storage for the 2021/20 winter.

Gas consumption has fallen 40% compared with peacetime levels, while production has decreased by only 5%, he said.

Analysts have argued the stability of the Ukrainian gas system could be disrupted in the event of a halt to gas transit.

Gas reserves held in storage in western Ukraine would not be enough to maintain pressure in pipelines and fuel supplies to the east and centre of Ukraine, they said.

But Galushchenko said Kyiv was also ready for a move by Russia to cut gas transit through Ukraine.

"This is one of the scenarios and it is calculated. We will certainly survive," the minister said, adding it is a possible and obvious scenario.

Since the beginning of the year, Russia has reduced gas transit via Ukraine. Those volumes averaged about 40-42 million cubic meters per day in August, despite Russian gas supplier Gazprom paying Kyiv to pump 109 million a day.

(Editing by Tom Balmforth and Josie Kao)