Moldova has the Fort Knox of red wine. At Mileștii Mici, the world’s largest wine cellar, 120 miles of passages connect limestone galleries where 2 million bottles age in silence. Yet, with war raging above ground, Ukrainian and Russian military commanders are more interested in Moldova’s role as home to the largest Soviet-era ammunition stocks in Europe — about 20,000 tons.

In the late 1940s, Stalin prepared for a confrontation with the West by forward positioning massive amounts of ammunition and weapons in Cobasna, a Moldovan village on an east-west rail line. Not trusting his Warsaw Pact allies, Stalin also stored military materiel for East Germany and Czechoslovakia. 

Today, these three states no longer exist. But two successor states, Russia and Ukraine, are waging such a fierce war that both face ammunition shortages. On Sunday, the boss of Russia’s Wagner mercenary group, Yevgeny Prigozhin, wrote the Russian commander of the Ukraine campaign “about the urgent need to allocate ammunition.”

Without more ammo, Mr. Prigozhin warned, Russia’s offensive to take Bakhmut, could fail. Now, Russians and Ukrainians eye Cobasna, located in a pocket, surrounded by Ukraine on two sides. This vast ammo dump, though, is marooned, cut off from the war raging about 500 miles to the east.

Russia controls Cobasna, a village on the northern tip of Transnistria. This 200-mile long breakaway republic, is populated by 360,000 Russian-speakers and protected by about 100 Russian officers and 1,500 Russian Army soldiers recruited from the local population.  Russia controls Transnistria, but it cannot move the ammunition east through Ukraine, or west through neutral Moldova.

After Russia attacked Ukraine a year ago, Ukraine closed all border crossings with Transnistria. Historically, Transnistria’s exports flowed south to Odessa, a major Ukrainian Black Sea port. In the 1990s, when the Soviet Union was awash with weapons, supplies from Cobasna were reportedly trafficked through Odessa. Hollywood captured this trade in the 2005 Nicholas Cage film, “Lord of War.”

In April, when the war was going well for Russia, a top Russian commander, Major General Rustam Minnekayev, said: “Russian control over the south of Ukraine is another way out to Transnistria, where there are cases of Russian-speaking people being oppressed.” He said a Russian military takeover of Odessa city and region would restore Transnistria’s access to Odessa port. 

At the time, Transnistrian officials protested that Ukraine had sent reconnaissance drones over the Cobasna storage area and shots were fired into the village. Ukraine dismissed the reports as part of a “false flag” operation designed to justify a Russian takeover of Moldova.

More recently, American and Ukrainian officials warned that Russia is taking a political tack. It seeks to fuel a popular uprising or coup d’etat in Moldova. Early last month, President Zelensky said Ukraine intercepted “a detailed Russian plan to destroy the political situation in Moldova.”

Mr. Zelensky’s adviser, Mykhailo Podolyak, said Russia is trying to seize power in Moldova, just as it did a year ago in Ukraine. He told Moldova’s Tv8: “But in Moldova, Russia wants to do things differently — not by tanks, but by bandits.” 

Russia denies those claims. The Foreign Ministry spokeswoman, Maria Zakharova, said the allegations were “absolutely unfounded and unsubstantiated.” Her boss, Russia’s foreign minister, Sergei Lavrov, warned that the West wants Moldova “to play the role of the next Ukraine.”

Two weeks ago, Secretary of State Blinken met in Munich with Moldova’s pro-Western president, Maia Sandhu. Later, Mr. Blinken said America is alarmed by “some of the plotting that we’ve seen coming from Russia to try to destabilize the government.” Mr. Blinken said that America would continue to “stand strongly with Moldova in support of its security, its independence, its territorial integrity.” 

Five days later, President Biden met with Ms. Sandhu at Warsaw. The White House reported: “President Biden reaffirmed strong U.S. support for Moldova’s sovereignty and territorial integrity.” But there may be more to the political moves than shadow boxing.

After Ukraine moved soldiers to the Moldovan border, Russia’s Defense Ministry charged two weeks ago that Ukraine was preparing to take over Transnistria to grab the arms. The Moldovan government quickly said that it “does not confirm the information disseminated this morning by the Russian Ministry of Defense.” Ukraine did not comment.

Cobasna has long been closed to civilian visitors. Aerial photos show cement casements separating stocks. Closeup ground photos show outdoor pyramids of rusting, Soviet-era torpedoes. Other photos seem to show fortified casements with wooden crates of well-oiled Kalashnikovs. 

According to a Tweet last week by a group called OSINTdefender, Russian officers have wired the depot to blow up in the event of a Ukrainian attack. In 2015, the Academy of Sciences of Moldova calculated that mass of aging ammunition could explode with a force comparable to “the size of the atomic bombs dropped on both Hiroshima and Nagasaki.”

In Transnistria, uneasiness is spreading. According to Ukrainian Military Intelligence, more and more Transnistrian men refuse to sign enlistment contracts with the Russian Army. According to a Transnistrian-focused research center in Moldova, Zona de Securitate, the number of Transnistrians requesting Moldovan identity documents has doubled. Since 2014, Moldovans have enjoyed visa-free entry to the EU.