Russian air defences shot down 31 Ukrainian drones during a concerted night-time attack by Kyiv’s forces on border regions, the Russian defence ministry said on Wednesday, even as uncertainty grew over Ukraine’s future access to weapons and ammunition from its western allies.

The drone attack appeared to be Kyiv’s largest single cross-border drone assault reported by Moscow since it launched its invasion 20 months ago.

Ukraine is pressing on with a slow-moving counteroffensive it launched three months ago, though mounting concerns about replenishing its military stocks cast a cloud over its efforts

Admiral Rob Bauer, the head of Nato’s Military Committee, sounded the alarm about depleted stockpiles.

With the war of attrition likely continuing through winter into next year, Bauer said of weapons systems and ammunition supplies: “The bottom of the barrel is now visible.”

He urged the defence industry to boost production “at a much higher tempo. And we need large volumes,” he told the Warsaw Security Forum, an annual two-day conference that continued on Wednesday.

The Russian defence ministry didn’t provide any evidence for its claims about intercepting Ukrainian drones nor any details about whether there were any damage or casualties. It also said Russian aircraft thwarted a Ukrainian attempt to deploy a group of soldiers by sea to the western side of Crimea.

The force tried to land on Cape Tarkhankut, on Crimea’s western end, using a boat and jet skis, the ministry said. Moscow’s claims could not be independently verified, and Ukrainians made no comment.