Russia said Tuesday its forces had captured 400 square kilometres (150 square miles) of Ukrainian territory this year.

Moscow secured its first territorial gains in almost a year in recent months, as Kyiv struggles with manpower and ammunition shortages amid delays to vital Western aid.

"Since the start of the year, 403 square kilometres ... have come under our control," Defence Minister Sergei Shoigu said, referring to gains in the Donetsk, Kherson, Lugansk and Zaporizhzhia regions that Moscow claimed to have annexed in 2022, despite not fully controlling them.

"Russian armed forces continue to push Ukrainian units westwards," Shoigu told a meeting of Russia's military chiefs, according to a transcript published by the defence ministry.

In February, Russia captured the frontline town of Avdiivka, just outside the Russian-held regional capital of Donetsk city in its most significant territorial advance since May last year.

Shoigu said Russian forces had captured five settlements -- four in Donetsk and one in Zaporizhzhia -- over the last month.

The Institute for the Study of War (ISW) said last week that the recent acceleration in Russian gains on the battlefield was "not reflective of the threat of Russian operational success amid continued delays in US security assistance" to Kyiv.

It said Ukraine faced "materiel constraints" on its defensive capabilities.

A $60 billion package of military support is held up in the US Congress, while promised deliveries of artillery shells from Europe to Ukraine are running behind schedule.

The ISW estimates Russia controls more than 100,000 square kilometres -- or almost a fifth -- of Ukrainian territory.