Russia says it has taken control of settlements near the key city of Avdiivka in Ukraine's eastern Donetsk region, in an apparent aim to step up its offensive before Ukrainian forces can rebuild its defense line.

Russian Defense Minister Sergei Shoigu said at a meeting on Tuesday that his country had seized settlements including Severne in the past week.

A US think tank, the Institute for the Study of War, said that Shoigu is likely taking advantage of recent tactical gains in Avdiivka ahead of the Russian presidential election in March.

The institute assessed that Russian forces appear to be maintaining a high intensity of offensive operations aimed at pushing ahead as far as possible in the Avdiivka area before Ukrainian forces re-establish their defense lines.

In recent weeks, Ukrainian forces have said they had shot down several Russian military planes. Last Friday, Kyiv announced its air force had shot down a key Russian A-50 early warning and control aircraft, vital to Russia's operations.

Ukrainian Air Force spokesperson Yurii Ihnat said on Tuesday that Russia has not deployed its A-50 aircraft for days, suggesting that the downing of the plane was affecting Russia's tactics.

The UK defense ministry said in its intelligence update on the same day that the A-50 was most likely destroyed by a surface-to-air missile. It also said that Russia had lost two of its nine operational A-50s in two months.

The ministry points out that the loss of two experienced specialist mission crews will force the Russian air force to reconsider the operating locations for its A-50 aircraft. The ministry also said that Ukrainian air strikes continue to pose a threat to the Russian side.