WASHINGTON (AP) — Weapons shortages across Europe could force hard choices for Ukraine’s allies as they balance their support for Ukraine against the risk that Russia could target them next.

For months, the United States and other NATO members have sent billions of dollars worth of weapons and equipment into Ukraine to help it fight back against Russia. But, for many of the smaller NATO countries, and even some of the larger ones, the war has strained already-depleted weapons stockpiles. Some allies sent all their reserve Soviet-era weaponry and are now waiting for US replacements.

It can be difficult for some European countries to rapidly resupply because they no longer have a strong defense sector to quickly build replacements, with many relying on a dominant American defense industry that has elbowed out some foreign competitors.

Now they face a dilemma: Do they keep sending their stocks of weapons to Ukraine and potentially increase their own vulnerability to Russian attack or do they hold back what’s left to protect their homeland, risking the possibility that makes a Russian victory in Ukraine more likely?

It’s a tough calculation.

After eight months of intense fighting, the allies expect the war will continue for months, maybe years, with both sides rapidly using up weapons supplies. Victory may come down to who can last longer.

The stockpile strain comes up “all the time,” especially among smaller NATO countries, said Defense Minister Hanno Pevkur of Estonia, a Baltic nation that shares a 183-mile (295-kilometer) border with Russia.

It weighs on them even as Defense Secretary Lloyd Austin has urged members of the Western alliance, at a recent NATO gathering in Brussels, “to dig deep and provide additional capability” to Ukraine.

European officials, in public comments and interviews with The Associated Press, said Russia must not be allowed to win in Ukraine and that their support will continue. But they stressed that domestic defense is weighing on them all.

“Our estimation is that Russia will restore their capabilities sooner rather than later” because Russian President Vladimir Putin can order weapons makers to go into 24-hour a day production, Pevkur said.

Russia has directed some troops to factories instead of the front line, he said. The minister said Russia has a track record of reconstituting its military so it can launch invasions against European neighbors every few years, citing moves against Georgia in 2008, Ukraine’s Black Sea peninsula of Crimea in 2014 and now all of Ukraine this year.

“So the question is, ‘How much risk are you ready to take?’” Pevkur said at a German Marshall Fund event this past week.

Other smaller nations, such as fellow Baltic state Lithuania, face the same challenges. But so do some larger NATO members, including Germany.

“Ukraine has led to a general shortage of supply because so many states have forgotten that conventional war is burning through your ammunition reserve. Just burning through it,” Dovilė Šakalienė, a member of Lithuania’s Parliament, said in a phone interview. “In certain situations, even the word ‘excess’ is not applicable. In certain situations, we left ourselves with a bare minimum.”

Germany faces a similar situation, the ministry of defense said in an email to the AP. “Yes, the Bundeswehr’s stocks are limited. Just as it is the case in other European countries,” the ministry said.