Ukraine's army chief Oleksandr Syrskyi said on Friday he would strengthen troops deployed on the eastern front with reserves, ammunition and equipment after he visited two key Ukrainian-held sites in the Donetsk region.

Russian forces are advancing in the Donetsk region at the fastest rate since the early days of the 2022 invasion, and the defense ministry in Moscow on Friday claimed control of two new settlements there.

But Syrskyi said Ukrainian forces were continuing to repel Russian advances after he paid a visit to units near the towns of Pokrovsk and Kurakhhove.

"Based on the results of the work, all necessary decisions have been made to strengthen the units with reserves, additional ammunition, weapons, and military equipment," he said on the Telegram messaging app.

"We continue to restrain the enemy and inflict heavy losses in terms of their manpower and equipment."

The war against Russia has reached a critical juncture.

Russian President Vladimir Putin has threatened to target Ukraine's "decision-making centers" with its new ballistic missile in response to Kyiv using Western-supplied missiles to strike back inside Russia.