Advancing in some areas of the Donetsk region is difficult, the top Moscow-installed official in the occupied parts of the territory in eastern Ukraine said on Tuesday, adding that more than half was under Russian control.

The so-called Donetsk People’s Republic is one of four regions in Ukraine which Moscow proclaimed as its own in September in an exercise Ukraine and its allies denounced as a “sham,” coercive referendum.

“A little more than 50% of the territory of the Donetsk People’s Republic has been liberated,” Denis Pushilin, Russian-installed administrator of the portion controlled by Moscow, told Russian state-owned news agency RIA.

Reuters was unable to independently verify the report.

Fierce fighting in the region in recent weeks has left unclear which parts of Donetsk are under Russian and Ukrainian control.

Russia has claimed to be gradually advancing its positions, with the defence ministry saying on Monday that its offensive there had killed 30 Ukrainian military personnel the day before.

However, Pushilin said the situation was tough along the Lyman line of contact in the region’s north. Ukraine had liberated Lyman hours after Putin proclaimed the annexation of Donetsk in September.

“The situation remains difficult, the enemy is trying to counterattack, but our units are now holding all positions,”

RIA cited Pushilin as saying. “It is not always possible to move forward.”

Russia’s sustained shelling of the frontline in Donetsk has completely destroyed the city of Bakhmut and heavily damaged the city of Avdiivka, which lies in the region’s centre, Ukraine’s President Volodymyr Zelenskiy said on Friday.

On Monday, the general staff of Ukraine’s armed forces said Russia kept concentrating its efforts to advance and capture both cities.

“Near Bakhmut, the occupiers rained mortar and artillery fire on nearly 20 settlements,” it said in a daily evening update.

Nine settlements came under shelling near Avdiivka, the military said.

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Britain’s defence ministry said Russia was still likely to be planning deeper advances within Donetsk, but cast doubts on its ability to do so.

“It is highly unlikely that the Russian military is currently able to generate an effective striking force capable of retaking these areas,” it said.

“Russian ground forces are unlikely to make operationally significant advances within the next several months.”