Ukrainian officials reported heavy fighting in eastern regions on Thursday as Kyiv's forces tried to push back Russian troops, while President Volodymyr Zelenskyy urged the West to provide his army with heavy tanks.

The Ukrainian military said the Russians were focused on an offensive in the Bakhmut sector in Donetsk region, but their attacks in the Avdiivka and Kupiansk sectors were unsuccessful.

The governor of Luhansk region said Ukrainian troops were recapturing areas "step-by-step." But he added: "It is not happening fast."

A senior U.S. administration official on Wednesday predicted a long road ahead in a war that has now raged for nearly 11 months.

"The fighting is still quite hot (in Donetsk)... what we're seeing in Bakhmut we should expect to see elsewhere along the front, that there will be continued fighting in the coming months," the official said in Washington.

The Luhansk governor, Serhiy Haidai, said he expected fighting to intensify as temperatures drop further and the ground freezes.

"Then the opportunity to use heavy equipment will open up," he said.

In his evening video address, Zelenskyy urged Western allies to provide his army with tanks and heavy weapons to combat the Russian forces, who invaded his country last February.

French President Emmanuel Macron said on Wednesday his government would send light AMX-10 RC armored combat vehicles to help its war effort.

Zelenskyy thanked Macron but said: "There is no rational reason why Ukraine has not yet been supplied with Western tanks."

The Ukrainian leader also said his troops outside Russian-occupied Bakhmut were inflicting numerous losses on their adversaries and Russia was building up its forces in the region.

Ukraine's military said on Thursday it estimated 800 Russian soldiers were killed in the past day, mostly in fighting in the Donetsk region. The figure - which would signify a huge loss of life for a single day - could not be independently confirmed.

The military also said one Russian aircraft, a helicopter and three tanks had been destroyed over the past day.

Russian air, missile and rocket attacks on the largely ruined Bakhmut and two other cities in Donetsk - Kostiantynivka and Kurakhove - had caused an unspecified number of civilian casualties, it said.

Russia denies targeting civilians in what it calls its special military operation in Ukraine. Reuters could not independently verify battlefield accounts.