Russia is running short of precision missiles in its war against Ukraine and its arms factories lack the ability to produce enough to keep up with demand, western officials have said.

Limitations in Russia’s arms supply industry and the impact of western sanctions mean Moscow is having to transport missiles from other parts of the country to Ukraine, the officials said on Friday.

“Their stock is limited, it is being run down, and we are seeing them having to move Kalibr missiles from other strategic directions where they may be stored,” said one western official, referring to sea-launched cruise missiles. “That brings you some indications that their stock of precision weapons is being reduced.”

The assessment comes as the US and its European allies boost efforts to arm Kyiv and are girding for a protracted conflict, with the Biden administration looking to send $33bn more in military, economic and humanitarian aid to Ukraine.

It also comes as the Kremlin continues to struggle on the ground in Ukraine, with the Pentagon saying it believes Russia is at least several days behind its goal to encircle Ukrainian forces in the Donbas region.

“We believe that they meant to be much further along in terms of a total encirclement of Ukrainian troops in the east and they have not been able to link north with south,” said a senior US defence official. “In fact they’re nowhere close to linking north with south as the Ukrainians continue to fight back.”

Most Russian strikes are concentrated in the eastern Donbas region and the coastal city of Mariupol, the US official said, adding that most of the ordinance is “dumb ordinance, not precision-guided”.

“We think that speaks to challenges that the Russians are having with [precision-guided munitions] replenishment,” the US official said.