Half of Western military aid to Kyiv is delivered late, Ukrainian Defence Minister Rustem Umerov said on Sunday.

Ukraine, which is struggling with an ammunition shortage, has for months said that Western aid is slow to reach it and this has real consequences for its two-year fight against Russia.

"At the moment, commitment does not constitute delivery," Umerov said during a forum dedicated to the second anniversary of Russia's invasion of its neighbour.

"Fifty percent of commitments are not delivered on time," he added.

Umerov argued this put Ukraine at a further disadvantage "in the mathematics of war" against Russia, which the West has said is increasingly building a war economy.

Umerov said that delayed aid will mean Kyiv will "lose people, lose territories", especially given Russia's "air superiority".

"We do everything possible and impossible but without timely supply it harms us," he said.

Kyiv has in recent weeks been weakened by an ammunition shortage and vital US aid remains blocked by political wrangling in the US Congress.